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 $234.92   12.789%   $264.9639   $264.96   $264.95   $265.00  
  Purchase #2 $23.62   7.293%   $25.3426   $25.34   $25.35   $25.30  
  Purchase #3 $16.54   8.305%   $17.9136   $17.91   $17.90   $17.90  
  Purchase #4 $162.34   7.153%   $173.9522   $173.95   $173.95   $174.00  
  Purchase #5 $134.62   11.466%   $150.0555   $150.06   $150.05   $150.10  
  Purchase #6 $221.40   11.690%   $247.2817   $247.28   $247.30   $247.30  
  Purchase #7 $101.26   6.109%   $107.446   $107.45   $107.45   $107.40  
  7 purchase totals = $894.70       $986.9555   $986.95   $986.95   $987.00