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 $30.59   6.411%   $32.5511   $32.55   $32.55   $32.60  
  Purchase #2 $185.49   5.185%   $195.1077   $195.11   $195.10   $195.10  
  Purchase #3 $132.45   9.374%   $144.8659   $144.87   $144.85   $144.90  
  Purchase #4 $156.51   5.609%   $165.2886   $165.29   $165.30   $165.30  
  Purchase #5 $58.80   6.561%   $62.6579   $62.66   $62.65   $62.70  
  Purchase #6 $227.26   11.685%   $253.8153   $253.82   $253.80   $253.80  
  Purchase #7 $142.86   6.339%   $151.9159   $151.92   $151.90   $151.90  
  7 purchase totals = $933.96       $1,006.2024   $1,006.22   $1,006.15   $1,006.30