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 $225.85   9.344%   $246.9534   $246.95   $246.95   $247.00  
  Purchase #2 $31.79   12.770%   $35.8496   $35.85   $35.85   $35.80  
  Purchase #3 $69.84   9.120%   $76.2094   $76.21   $76.20   $76.20  
  Purchase #4 $219.56   4.597%   $229.6532   $229.65   $229.65   $229.70  
  Purchase #5 $224.60   9.871%   $246.7703   $246.77   $246.75   $246.80  
  Purchase #6 $175.61   10.693%   $194.388   $194.39   $194.40   $194.40  
  Purchase #7 $139.62   8.647%   $151.6929   $151.69   $151.70   $151.70  
  7 purchase totals = $1,086.87       $1,181.5168   $1,181.51   $1,181.50   $1,181.60