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 $66.65   3.260%   $68.8228   $68.82   $68.80   $68.80  
  Purchase #2 $228.87   8.165%   $247.5572   $247.56   $247.55   $247.60  
  Purchase #3 $167.85   9.112%   $183.1445   $183.14   $183.15   $183.10  
  Purchase #4 $149.31   3.507%   $154.5463   $154.55   $154.55   $154.50  
  Purchase #5 $94.32   5.733%   $99.7274   $99.73   $99.75   $99.70  
  Purchase #6 $227.82   9.736%   $250.0006   $250.00   $250.00   $250.00  
  Purchase #7 $146.84   3.799%   $152.4185   $152.42   $152.40   $152.40  
  7 purchase totals = $1,081.66       $1,156.2173   $1,156.22   $1,156.20   $1,156.10