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 $55.73   3.626%   $57.7508   $57.75   $57.75   $57.80  
  Purchase #2 $157.89   12.121%   $177.0278   $177.03   $177.05   $177.00  
  Purchase #3 $236.44   5.603%   $249.6877   $249.69   $249.70   $249.70  
  Purchase #4 $205.32   13.568%   $233.1778   $233.18   $233.20   $233.20  
  Purchase #5 $218.78   11.114%   $243.0952   $243.10   $243.10   $243.10  
  Purchase #6 $46.72   6.455%   $49.7358   $49.74   $49.75   $49.70  
  Purchase #7 $246.99   11.724%   $275.9471   $275.95   $275.95   $275.90  
  7 purchase totals = $1,167.87       $1,286.4222   $1,286.44   $1,286.50   $1,286.40