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 $225.97   7.654%   $243.2657   $243.27   $243.25   $243.30  
  Purchase #2 $130.78   6.534%   $139.3252   $139.33   $139.35   $139.30  
  Purchase #3 $8.57   7.575%   $9.2192   $9.22   $9.20   $9.20  
  Purchase #4 $160.55   8.335%   $173.9318   $173.93   $173.95   $173.90  
  Purchase #5 $60.25   6.464%   $64.1446   $64.14   $64.15   $64.10  
  Purchase #6 $120.63   12.604%   $135.8342   $135.83   $135.85   $135.80  
  Purchase #7 $161.98   11.123%   $179.997   $180.00   $180.00   $180.00  
  7 purchase totals = $868.73       $945.7177   $945.72   $945.75   $945.60