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 $183.76   11.342%   $204.6021   $204.60   $204.60   $204.60  
  Purchase #2 $245.77   9.854%   $269.9882   $269.99   $270.00   $270.00  
  Purchase #3 $68.64   8.857%   $74.7194   $74.72   $74.70   $74.70  
  Purchase #4 $167.34   4.330%   $174.5858   $174.59   $174.60   $174.60  
  Purchase #5 $43.65   13.256%   $49.4362   $49.44   $49.45   $49.40  
  Purchase #6 $24.35   4.762%   $25.5095   $25.51   $25.50   $25.50  
  Purchase #7 $124.57   13.848%   $141.8205   $141.82   $141.80   $141.80  
  7 purchase totals = $858.08       $940.6617   $940.67   $940.65   $940.60