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 $210.29   11.318%   $234.0906   $234.09   $234.10   $234.10  
  Purchase #2 $44.39   3.766%   $46.0617   $46.06   $46.05   $46.10  
  Purchase #3 $147.70   12.460%   $166.1034   $166.10   $166.10   $166.10  
  Purchase #4 $119.47   10.740%   $132.3011   $132.30   $132.30   $132.30  
  Purchase #5 $82.36   8.191%   $89.1061   $89.11   $89.10   $89.10  
  Purchase #6 $84.57   9.522%   $92.6228   $92.62   $92.60   $92.60  
  Purchase #7 $239.52   9.156%   $261.4505   $261.45   $261.45   $261.50  
  7 purchase totals = $928.30       $1,021.7362   $1,021.73   $1,021.70   $1,021.80