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 $99.35   9.593%   $108.8806   $108.88   $108.90   $108.90  
  Purchase #2 $125.33   11.310%   $139.5048   $139.50   $139.50   $139.50  
  Purchase #3 $155.41   6.219%   $165.0749   $165.07   $165.05   $165.10  
  Purchase #4 $163.67   12.178%   $183.6017   $183.60   $183.60   $183.60  
  Purchase #5 $34.53   11.205%   $38.3991   $38.40   $38.40   $38.40  
  Purchase #6 $87.36   5.400%   $92.0774   $92.08   $92.10   $92.10  
  Purchase #7 $104.51   3.709%   $108.3863   $108.39   $108.40   $108.40  
  7 purchase totals = $770.16       $835.9248   $835.92   $835.95   $836.00