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 $40.26   9.221%   $43.9724   $43.97   $43.95   $44.00  
  Purchase #2 $59.52   10.309%   $65.6559   $65.66   $65.65   $65.70  
  Purchase #3 $235.37   8.862%   $256.2285   $256.23   $256.25   $256.20  
  Purchase #4 $95.25   3.463%   $98.5485   $98.55   $98.55   $98.50  
  Purchase #5 $243.32   7.624%   $261.8707   $261.87   $261.85   $261.90  
  Purchase #6 $153.88   7.494%   $165.4118   $165.41   $165.40   $165.40  
  Purchase #7 $213.44   9.205%   $233.0872   $233.09   $233.10   $233.10  
  7 purchase totals = $1,041.04       $1,124.7750   $1,124.78   $1,124.75   $1,124.80