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 $60.77   8.456%   $65.9087   $65.91   $65.90   $65.90  
  Purchase #2 $140.25   7.722%   $151.0801   $151.08   $151.10   $151.10  
  Purchase #3 $207.27   13.785%   $235.8422   $235.84   $235.85   $235.80  
  Purchase #4 $218.46   10.227%   $240.8019   $240.80   $240.80   $240.80  
  Purchase #5 $12.87   13.649%   $14.6266   $14.63   $14.65   $14.60  
  Purchase #6 $75.75   5.518%   $79.9299   $79.93   $79.95   $79.90  
  Purchase #7 $247.37   5.559%   $261.1213   $261.12   $261.10   $261.10  
  7 purchase totals = $962.74       $1,049.3107   $1,049.31   $1,049.35   $1,049.20