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 $166.79   4.357%   $174.057   $174.06   $174.05   $174.10  
  Purchase #2 $38.89   3.789%   $40.3635   $40.36   $40.35   $40.40  
  Purchase #3 $76.78   12.237%   $86.1756   $86.18   $86.20   $86.20  
  Purchase #4 $154.77   3.816%   $160.676   $160.68   $160.70   $160.70  
  Purchase #5 $94.53   8.152%   $102.2361   $102.24   $102.25   $102.20  
  Purchase #6 $66.57   3.494%   $68.896   $68.90   $68.90   $68.90  
  Purchase #7 $122.93   10.544%   $135.8917   $135.89   $135.90   $135.90  
  7 purchase totals = $721.26       $768.2959   $768.31   $768.35   $768.40