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 $46.66   6.475%   $49.6812   $49.68   $49.70   $49.70  
  Purchase #2 $178.59   9.144%   $194.9203   $194.92   $194.90   $194.90  
  Purchase #3 $242.93   7.710%   $261.6599   $261.66   $261.65   $261.70  
  Purchase #4 $106.58   12.785%   $120.2063   $120.21   $120.20   $120.20  
  Purchase #5 $41.46   10.268%   $45.7171   $45.72   $45.70   $45.70  
  Purchase #6 $117.61   6.845%   $125.6604   $125.66   $125.65   $125.70  
  Purchase #7 $205.43   6.632%   $219.0541   $219.05   $219.05   $219.10  
  7 purchase totals = $939.26       $1,016.8993   $1,016.90   $1,016.85   $1,017.00