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 $84.95   13.392%   $96.3265   $96.33   $96.35   $96.30  
  Purchase #2 $92.43   7.130%   $99.0203   $99.02   $99.00   $99.00  
  Purchase #3 $220.68   5.312%   $232.4025   $232.40   $232.40   $232.40  
  Purchase #4 $49.59   7.798%   $53.457   $53.46   $53.45   $53.50  
  Purchase #5 $57.44   6.330%   $61.076   $61.08   $61.10   $61.10  
  Purchase #6 $107.31   12.836%   $121.0843   $121.08   $121.10   $121.10  
  Purchase #7 $159.83   8.302%   $173.0991   $173.10   $173.10   $173.10  
  7 purchase totals = $772.23       $836.4657   $836.47   $836.50   $836.50