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 $60.56   9.715%   $66.4434   $66.44   $66.45   $66.40  
  Purchase #2 $186.65   13.497%   $211.8422   $211.84   $211.85   $211.80  
  Purchase #3 $215.31   12.815%   $242.902   $242.90   $242.90   $242.90  
  Purchase #4 $226.83   4.629%   $237.33   $237.33   $237.35   $237.30  
  Purchase #5 $126.64   13.172%   $143.321   $143.32   $143.30   $143.30  
  Purchase #6 $161.63   8.231%   $174.9338   $174.93   $174.95   $174.90  
  Purchase #7 $187.86   7.608%   $202.1524   $202.15   $202.15   $202.20  
  7 purchase totals = $1,165.48       $1,278.9248   $1,278.91   $1,278.95   $1,278.80