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 $195.47   11.712%   $218.3634   $218.36   $218.35   $218.40  
  Purchase #2 $237.49   9.712%   $260.555   $260.56   $260.55   $260.60  
  Purchase #3 $239.57   11.217%   $266.4426   $266.44   $266.45   $266.40  
  Purchase #4 $72.88   11.767%   $81.4558   $81.46   $81.45   $81.50  
  Purchase #5 $212.78   6.242%   $226.0617   $226.06   $226.05   $226.10  
  Purchase #6 $49.85   9.575%   $54.6231   $54.62   $54.60   $54.60  
  Purchase #7 $154.42   3.765%   $160.2339   $160.23   $160.25   $160.20  
  7 purchase totals = $1,162.46       $1,267.7355   $1,267.73   $1,267.70   $1,267.80