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 $87.78   4.861%   $92.047   $92.05   $92.05   $92.00  
  Purchase #2 $69.40   5.232%   $73.031   $73.03   $73.05   $73.00  
  Purchase #3 $199.94   11.726%   $223.385   $223.39   $223.40   $223.40  
  Purchase #4 $209.82   5.728%   $221.8385   $221.84   $221.85   $221.80  
  Purchase #5 $176.40   5.423%   $185.9662   $185.97   $185.95   $186.00  
  Purchase #6 $27.73   4.304%   $28.9235   $28.92   $28.90   $28.90  
  Purchase #7 $127.52   5.160%   $134.1   $134.10   $134.10   $134.10  
  7 purchase totals = $898.59       $959.2912   $959.30   $959.30   $959.20