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 $87.81   8.515%   $95.287   $95.29   $95.30   $95.30  
  Purchase #2 $110.34   12.836%   $124.5032   $124.50   $124.50   $124.50  
  Purchase #3 $165.66   9.695%   $181.7207   $181.72   $181.70   $181.70  
  Purchase #4 $64.29   13.837%   $73.1858   $73.19   $73.20   $73.20  
  Purchase #5 $197.33   8.410%   $213.9255   $213.93   $213.95   $213.90  
  Purchase #6 $166.69   5.164%   $175.2979   $175.30   $175.30   $175.30  
  Purchase #7 $119.31   8.237%   $129.1376   $129.14   $129.15   $129.10  
  7 purchase totals = $911.43       $993.0577   $993.07   $993.10   $993.00