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 $128.98   4.123%   $134.2978   $134.30   $134.30   $134.30  
  Purchase #2 $168.56   4.627%   $176.3593   $176.36   $176.35   $176.40  
  Purchase #3 $58.66   3.617%   $60.7817   $60.78   $60.80   $60.80  
  Purchase #4 $45.66   9.483%   $49.9899   $49.99   $50.00   $50.00  
  Purchase #5 $217.67   5.249%   $229.0955   $229.10   $229.10   $229.10  
  Purchase #6 $65.86   11.600%   $73.4998   $73.50   $73.50   $73.50  
  Purchase #7 $209.70   4.795%   $219.7551   $219.76   $219.75   $219.80  
  7 purchase totals = $895.09       $943.7791   $943.79   $943.80   $943.90