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 $87.77   9.173%   $95.8211   $95.82   $95.80   $95.80  
  Purchase #2 $57.94   12.752%   $65.3285   $65.33   $65.35   $65.30  
  Purchase #3 $168.62   10.804%   $186.8377   $186.84   $186.85   $186.80  
  Purchase #4 $64.71   5.497%   $68.2671   $68.27   $68.25   $68.30  
  Purchase #5 $206.64   9.535%   $226.3431   $226.34   $226.35   $226.30  
  Purchase #6 $93.80   12.806%   $105.812   $105.81   $105.80   $105.80  
  Purchase #7 $243.27   11.545%   $271.3555   $271.36   $271.35   $271.40  
  7 purchase totals = $922.75       $1,019.7650   $1,019.77   $1,019.75   $1,019.70