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 $186.86   5.119%   $196.4254   $196.43   $196.45   $196.40  
  Purchase #2 $13.29   11.595%   $14.831   $14.83   $14.85   $14.80  
  Purchase #3 $112.91   6.546%   $120.3011   $120.30   $120.30   $120.30  
  Purchase #4 $232.72   10.847%   $257.9631   $257.96   $257.95   $258.00  
  Purchase #5 $245.62   6.315%   $261.1309   $261.13   $261.15   $261.10  
  Purchase #6 $11.83   11.426%   $13.1817   $13.18   $13.20   $13.20  
  Purchase #7 $11.39   5.209%   $11.9833   $11.98   $12.00   $12.00  
  7 purchase totals = $814.62       $875.8165   $875.81   $875.90   $875.80