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 $227.70   6.103%   $241.5965   $241.60   $241.60   $241.60  
  Purchase #2 $28.87   13.383%   $32.7337   $32.73   $32.75   $32.70  
  Purchase #3 $146.68   7.571%   $157.7851   $157.79   $157.80   $157.80  
  Purchase #4 $76.54   13.203%   $86.6456   $86.65   $86.65   $86.60  
  Purchase #5 $147.31   13.338%   $166.9582   $166.96   $166.95   $167.00  
  Purchase #6 $136.67   11.815%   $152.8176   $152.82   $152.80   $152.80  
  Purchase #7 $212.86   5.371%   $224.2927   $224.29   $224.30   $224.30  
  7 purchase totals = $976.63       $1,062.8294   $1,062.84   $1,062.85   $1,062.80