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 $55.52   13.874%   $63.2228   $63.22   $63.20   $63.20  
  Purchase #2 $215.95   4.803%   $226.3221   $226.32   $226.30   $226.30  
  Purchase #3 $250.97   4.359%   $261.9098   $261.91   $261.90   $261.90  
  Purchase #4 $41.72   7.801%   $44.9746   $44.97   $44.95   $45.00  
  Purchase #5 $152.35   11.823%   $170.3623   $170.36   $170.35   $170.40  
  Purchase #6 $218.85   7.321%   $234.872   $234.87   $234.85   $234.90  
  Purchase #7 $105.69   6.707%   $112.7786   $112.78   $112.80   $112.80  
  7 purchase totals = $1,041.05       $1,114.4422   $1,114.43   $1,114.35   $1,114.50