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 $67.94   12.414%   $76.3741   $76.37   $76.35   $76.40  
  Purchase #2 $90.95   7.332%   $97.6185   $97.62   $97.60   $97.60  
  Purchase #3 $14.42   6.410%   $15.3443   $15.34   $15.35   $15.30  
  Purchase #4 $231.52   4.449%   $241.8203   $241.82   $241.80   $241.80  
  Purchase #5 $243.30   7.380%   $261.2555   $261.26   $261.25   $261.30  
  Purchase #6 $232.70   6.187%   $247.0971   $247.10   $247.10   $247.10  
  Purchase #7 $155.86   10.574%   $172.3406   $172.34   $172.35   $172.30  
  7 purchase totals = $1,036.69       $1,111.8504   $1,111.85   $1,111.80   $1,111.80