Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $246.97   11.163%   $274.5393   $274.54   $274.55   $274.50  
  Purchase #2 $221.80   8.589%   $240.8504   $240.85   $240.85   $240.90  
  Purchase #3 $195.67   12.853%   $220.8195   $220.82   $220.80   $220.80  
  Purchase #4 $156.50   5.824%   $165.6146   $165.61   $165.60   $165.60  
  Purchase #5 $240.48   13.787%   $273.635   $273.64   $273.65   $273.60  
  Purchase #6 $130.91   11.161%   $145.5209   $145.52   $145.50   $145.50  
  Purchase #7 $218.66   9.633%   $239.7235   $239.72   $239.70   $239.70  
  7 purchase totals = $1,410.99       $1,560.7032   $1,560.70   $1,560.65   $1,560.60