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 $57.28   7.641%   $61.6568   $61.66   $61.65   $61.70  
  Purchase #2 $137.67   3.868%   $142.9951   $143.00   $143.00   $143.00  
  Purchase #3 $189.92   10.693%   $210.2281   $210.23   $210.25   $210.20  
  Purchase #4 $160.60   6.209%   $170.5717   $170.57   $170.55   $170.60  
  Purchase #5 $48.36   9.694%   $53.048   $53.05   $53.05   $53.00  
  Purchase #6 $240.29   5.335%   $253.1095   $253.11   $253.10   $253.10  
  Purchase #7 $55.29   13.467%   $62.7359   $62.74   $62.75   $62.70  
  7 purchase totals = $889.41       $954.3451   $954.36   $954.35   $954.30