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 $168.54   8.761%   $183.3058   $183.31   $183.30   $183.30  
  Purchase #2 $234.32   7.141%   $251.0528   $251.05   $251.05   $251.10  
  Purchase #3 $152.91   13.151%   $173.0192   $173.02   $173.00   $173.00  
  Purchase #4 $246.97   11.426%   $275.1888   $275.19   $275.20   $275.20  
  Purchase #5 $10.67   7.703%   $11.4919   $11.49   $11.50   $11.50  
  Purchase #6 $17.52   13.438%   $19.8743   $19.87   $19.85   $19.90  
  Purchase #7 $134.45   8.798%   $146.2789   $146.28   $146.30   $146.30  
  7 purchase totals = $965.38       $1,060.2117   $1,060.21   $1,060.20   $1,060.30