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 $198.37   10.644%   $219.4845   $219.48   $219.50   $219.50  
  Purchase #2 $77.54   6.440%   $82.5336   $82.53   $82.55   $82.50  
  Purchase #3 $237.89   12.783%   $268.2995   $268.30   $268.30   $268.30  
  Purchase #4 $149.34   4.529%   $156.1036   $156.10   $156.10   $156.10  
  Purchase #5 $225.92   10.359%   $249.3231   $249.32   $249.30   $249.30  
  Purchase #6 $232.62   12.475%   $261.6393   $261.64   $261.65   $261.60  
  Purchase #7 $205.58   12.130%   $230.5169   $230.52   $230.50   $230.50  
  7 purchase totals = $1,327.26       $1,467.9005   $1,467.89   $1,467.90   $1,467.80