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 $206.93   9.573%   $226.7394   $226.74   $226.75   $226.70  
  Purchase #2 $23.87   6.107%   $25.3277   $25.33   $25.35   $25.30  
  Purchase #3 $92.83   6.465%   $98.8315   $98.83   $98.85   $98.80  
  Purchase #4 $47.63   4.819%   $49.9253   $49.93   $49.95   $49.90  
  Purchase #5 $148.86   5.345%   $156.8166   $156.82   $156.80   $156.80  
  Purchase #6 $161.55   6.552%   $172.1348   $172.13   $172.15   $172.10  
  Purchase #7 $119.50   9.524%   $130.8812   $130.88   $130.90   $130.90  
  7 purchase totals = $801.17       $860.6565   $860.66   $860.75   $860.50