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 $205.79   10.206%   $226.7929   $226.79   $226.80   $226.80  
  Purchase #2 $245.59   3.105%   $253.2156   $253.22   $253.20   $253.20  
  Purchase #3 $53.90   9.589%   $59.0685   $59.07   $59.05   $59.10  
  Purchase #4 $156.62   12.781%   $176.6376   $176.64   $176.65   $176.60  
  Purchase #5 $212.34   11.391%   $236.5276   $236.53   $236.55   $236.50  
  Purchase #6 $128.35   7.463%   $137.9288   $137.93   $137.95   $137.90  
  Purchase #7 $236.52   13.304%   $267.9866   $267.99   $268.00   $268.00  
  7 purchase totals = $1,239.11       $1,358.1576   $1,358.17   $1,358.20   $1,358.10