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 $173.75   13.492%   $197.1924   $197.19   $197.20   $197.20  
  Purchase #2 $100.96   11.757%   $112.8299   $112.83   $112.85   $112.80  
  Purchase #3 $42.34   11.453%   $47.1892   $47.19   $47.20   $47.20  
  Purchase #4 $71.36   6.832%   $76.2353   $76.24   $76.25   $76.20  
  Purchase #5 $94.77   9.683%   $103.9466   $103.95   $103.95   $103.90  
  Purchase #6 $33.33   5.306%   $35.0985   $35.10   $35.10   $35.10  
  Purchase #7 $165.52   9.367%   $181.0243   $181.02   $181.00   $181.00  
  7 purchase totals = $682.03       $753.5162   $753.52   $753.55   $753.40