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 $232.28   13.112%   $262.7366   $262.74   $262.75   $262.70  
  Purchase #2 $24.72   11.251%   $27.5012   $27.50   $27.50   $27.50  
  Purchase #3 $220.63   3.245%   $227.7894   $227.79   $227.80   $227.80  
  Purchase #4 $66.26   12.468%   $74.5213   $74.52   $74.50   $74.50  
  Purchase #5 $192.73   10.449%   $212.8684   $212.87   $212.85   $212.90  
  Purchase #6 $176.73   6.439%   $188.1096   $188.11   $188.10   $188.10  
  Purchase #7 $180.35   4.105%   $187.7534   $187.75   $187.75   $187.80  
  7 purchase totals = $1,093.70       $1,181.2799   $1,181.28   $1,181.25   $1,181.30