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 $208.69   7.371%   $224.0725   $224.07   $224.05   $224.10  
  Purchase #2 $118.82   5.149%   $124.938   $124.94   $124.95   $124.90  
  Purchase #3 $5.46   11.728%   $6.1003   $6.10   $6.10   $6.10  
  Purchase #4 $173.79   11.785%   $194.2712   $194.27   $194.25   $194.30  
  Purchase #5 $30.44   11.110%   $33.8219   $33.82   $33.80   $33.80  
  Purchase #6 $57.68   9.445%   $63.1279   $63.13   $63.15   $63.10  
  Purchase #7 $127.52   5.654%   $134.73   $134.73   $134.75   $134.70  
  7 purchase totals = $722.40       $781.0618   $781.06   $781.05   $781.00