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 $247.87   7.270%   $265.8901   $265.89   $265.90   $265.90  
  Purchase #2 $119.97   10.514%   $132.5836   $132.58   $132.60   $132.60  
  Purchase #3 $89.54   11.434%   $99.778   $99.78   $99.80   $99.80  
  Purchase #4 $248.49   5.769%   $262.8254   $262.83   $262.85   $262.80  
  Purchase #5 $186.84   10.774%   $206.9701   $206.97   $206.95   $207.00  
  Purchase #6 $20.48   12.222%   $22.9831   $22.98   $23.00   $23.00  
  Purchase #7 $63.58   5.181%   $66.8741   $66.87   $66.85   $66.90  
  7 purchase totals = $976.77       $1,057.9044   $1,057.90   $1,057.95   $1,058.00