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 $176.86   4.186%   $184.2634   $184.26   $184.25   $184.30  
  Purchase #2 $158.97   10.844%   $176.2087   $176.21   $176.20   $176.20  
  Purchase #3 $52.39   6.484%   $55.787   $55.79   $55.80   $55.80  
  Purchase #4 $58.50   4.290%   $61.0097   $61.01   $61.00   $61.00  
  Purchase #5 $211.73   5.469%   $223.3095   $223.31   $223.30   $223.30  
  Purchase #6 $51.52   11.867%   $57.6339   $57.63   $57.65   $57.60  
  Purchase #7 $119.98   13.637%   $136.3417   $136.34   $136.35   $136.30  
  7 purchase totals = $829.95       $894.5539   $894.55   $894.55   $894.50