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 $58.83   6.439%   $62.6181   $62.62   $62.60   $62.60  
  Purchase #2 $77.82   11.811%   $87.0113   $87.01   $87.00   $87.00  
  Purchase #3 $204.29   8.725%   $222.1143   $222.11   $222.10   $222.10  
  Purchase #4 $111.87   12.827%   $126.2196   $126.22   $126.20   $126.20  
  Purchase #5 $217.74   9.571%   $238.5799   $238.58   $238.60   $238.60  
  Purchase #6 $139.51   8.242%   $151.0084   $151.01   $151.00   $151.00  
  Purchase #7 $147.88   10.744%   $163.7682   $163.77   $163.75   $163.80  
  7 purchase totals = $957.94       $1,051.3198   $1,051.32   $1,051.25   $1,051.30