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 $221.45   11.462%   $246.8326   $246.83   $246.85   $246.80  
  Purchase #2 $29.77   13.339%   $33.741   $33.74   $33.75   $33.70  
  Purchase #3 $45.63   6.750%   $48.71   $48.71   $48.70   $48.70  
  Purchase #4 $103.92   11.331%   $115.6952   $115.70   $115.70   $115.70  
  Purchase #5 $230.59   4.338%   $240.593   $240.59   $240.60   $240.60  
  Purchase #6 $224.54   10.195%   $247.4319   $247.43   $247.45   $247.40  
  Purchase #7 $71.65   11.206%   $79.6791   $79.68   $79.70   $79.70  
  7 purchase totals = $927.55       $1,012.6828   $1,012.68   $1,012.75   $1,012.60