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 $63.29   4.753%   $66.2982   $66.30   $66.30   $66.30  
  Purchase #2 $174.74   10.488%   $193.0667   $193.07   $193.05   $193.10  
  Purchase #3 $48.85   10.429%   $53.9446   $53.94   $53.95   $53.90  
  Purchase #4 $232.78   6.243%   $247.3125   $247.31   $247.30   $247.30  
  Purchase #5 $212.83   8.265%   $230.4204   $230.42   $230.40   $230.40  
  Purchase #6 $147.53   10.364%   $162.82   $162.82   $162.80   $162.80  
  Purchase #7 $41.76   7.301%   $44.8089   $44.81   $44.80   $44.80  
  7 purchase totals = $921.78       $998.6713   $998.67   $998.60   $998.60