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 $171.67   4.484%   $179.3677   $179.37   $179.35   $179.40  
  Purchase #2 $118.69   7.119%   $127.1395   $127.14   $127.15   $127.10  
  Purchase #3 $129.67   6.667%   $138.3151   $138.32   $138.30   $138.30  
  Purchase #4 $114.53   8.692%   $124.4849   $124.48   $124.50   $124.50  
  Purchase #5 $88.37   11.736%   $98.7411   $98.74   $98.75   $98.70  
  Purchase #6 $82.54   7.690%   $88.8873   $88.89   $88.90   $88.90  
  Purchase #7 $110.45   10.489%   $122.0351   $122.04   $122.05   $122.00  
  7 purchase totals = $815.92       $878.9707   $878.98   $879.00   $878.90