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 $49.72   11.211%   $55.2941   $55.29   $55.30   $55.30  
  Purchase #2 $138.76   11.219%   $154.3275   $154.33   $154.35   $154.30  
  Purchase #3 $68.27   9.498%   $74.7543   $74.75   $74.75   $74.80  
  Purchase #4 $181.38   9.429%   $198.4823   $198.48   $198.50   $198.50  
  Purchase #5 $29.82   9.591%   $32.68   $32.68   $32.70   $32.70  
  Purchase #6 $112.89   10.128%   $124.3235   $124.32   $124.30   $124.30  
  Purchase #7 $196.63   4.774%   $206.0171   $206.02   $206.00   $206.00  
  7 purchase totals = $777.47       $845.8788   $845.87   $845.90   $845.90