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 $56.82   9.578%   $62.2622   $62.26   $62.25   $62.30  
  Purchase #2 $126.80   7.354%   $136.1249   $136.12   $136.10   $136.10  
  Purchase #3 $141.52   10.550%   $156.4504   $156.45   $156.45   $156.50  
  Purchase #4 $111.80   6.743%   $119.3387   $119.34   $119.35   $119.30  
  Purchase #5 $103.75   10.311%   $114.4477   $114.45   $114.45   $114.40  
  Purchase #6 $44.72   9.731%   $49.0717   $49.07   $49.05   $49.10  
  Purchase #7 $175.61   12.471%   $197.5103   $197.51   $197.50   $197.50  
  7 purchase totals = $761.02       $835.2059   $835.20   $835.15   $835.20