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 $72.97   4.573%   $76.3069   $76.31   $76.30   $76.30  
  Purchase #2 $243.75   4.793%   $255.4329   $255.43   $255.45   $255.40  
  Purchase #3 $156.40   7.861%   $168.6946   $168.69   $168.70   $168.70  
  Purchase #4 $190.30   9.669%   $208.7001   $208.70   $208.70   $208.70  
  Purchase #5 $61.98   13.591%   $70.4037   $70.40   $70.40   $70.40  
  Purchase #6 $204.25   5.192%   $214.8547   $214.85   $214.85   $214.90  
  Purchase #7 $240.45   11.750%   $268.7029   $268.70   $268.70   $268.70  
  7 purchase totals = $1,170.10       $1,263.0958   $1,263.08   $1,263.10   $1,263.10