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 $105.56   10.856%   $117.0196   $117.02   $117.00   $117.00  
  Purchase #2 $61.71   8.520%   $66.9677   $66.97   $66.95   $67.00  
  Purchase #3 $141.31   6.645%   $150.7   $150.70   $150.70   $150.70  
  Purchase #4 $76.46   4.204%   $79.6744   $79.67   $79.65   $79.70  
  Purchase #5 $114.79   4.112%   $119.5102   $119.51   $119.50   $119.50  
  Purchase #6 $10.31   10.570%   $11.3998   $11.40   $11.40   $11.40  
  Purchase #7 $27.93   10.430%   $30.8431   $30.84   $30.85   $30.80  
  7 purchase totals = $538.07       $576.1148   $576.11   $576.05   $576.10