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 $51.25   13.327%   $58.0801   $58.08   $58.10   $58.10  
  Purchase #2 $204.79   3.135%   $211.2102   $211.21   $211.20   $211.20  
  Purchase #3 $59.77   4.228%   $62.2971   $62.30   $62.30   $62.30  
  Purchase #4 $53.52   13.306%   $60.6414   $60.64   $60.65   $60.60  
  Purchase #5 $112.74   10.407%   $124.4729   $124.47   $124.45   $124.50  
  Purchase #6 $85.46   9.278%   $93.389   $93.39   $93.40   $93.40  
  Purchase #7 $245.79   13.134%   $278.0721   $278.07   $278.05   $278.10  
  7 purchase totals = $813.32       $888.1628   $888.16   $888.15   $888.20