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 $141.44   6.362%   $150.4384   $150.44   $150.45   $150.40  
  Purchase #2 $22.38   9.239%   $24.4477   $24.45   $24.45   $24.40  
  Purchase #3 $239.73   8.625%   $260.4067   $260.41   $260.40   $260.40  
  Purchase #4 $55.95   11.155%   $62.1912   $62.19   $62.20   $62.20  
  Purchase #5 $62.26   3.227%   $64.2691   $64.27   $64.25   $64.30  
  Purchase #6 $245.28   12.603%   $276.1926   $276.19   $276.20   $276.20  
  Purchase #7 $191.96   13.852%   $218.5503   $218.55   $218.55   $218.60  
  7 purchase totals = $959.00       $1,056.4960   $1,056.50   $1,056.50   $1,056.50