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 $43.77   5.867%   $46.338   $46.34   $46.35   $46.30  
  Purchase #2 $70.34   10.719%   $77.8797   $77.88   $77.90   $77.90  
  Purchase #3 $48.39   9.578%   $53.0248   $53.02   $53.00   $53.00  
  Purchase #4 $77.99   4.591%   $81.5705   $81.57   $81.55   $81.60  
  Purchase #5 $138.99   5.706%   $146.9208   $146.92   $146.90   $146.90  
  Purchase #6 $220.48   10.755%   $244.1926   $244.19   $244.20   $244.20  
  Purchase #7 $198.74   5.629%   $209.9271   $209.93   $209.95   $209.90  
  7 purchase totals = $798.70       $859.8535   $859.85   $859.85   $859.80