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 $23.85   6.654%   $25.437   $25.44   $25.45   $25.40  
  Purchase #2 $113.55   13.568%   $128.9565   $128.96   $128.95   $129.00  
  Purchase #3 $155.83   13.805%   $177.3423   $177.34   $177.35   $177.30  
  Purchase #4 $238.93   9.636%   $261.9533   $261.95   $261.95   $262.00  
  Purchase #5 $154.79   7.797%   $166.859   $166.86   $166.85   $166.90  
  Purchase #6 $108.91   10.297%   $120.1245   $120.12   $120.10   $120.10  
  Purchase #7 $169.93   5.751%   $179.7027   $179.70   $179.70   $179.70  
  7 purchase totals = $965.79       $1,060.3753   $1,060.37   $1,060.35   $1,060.40