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 $38.58   6.483%   $41.0811   $41.08   $41.10   $41.10  
  Purchase #2 $103.98   4.423%   $108.579   $108.58   $108.60   $108.60  
  Purchase #3 $76.37   8.148%   $82.5926   $82.59   $82.60   $82.60  
  Purchase #4 $171.27   7.403%   $183.9491   $183.95   $183.95   $183.90  
  Purchase #5 $233.75   11.378%   $260.3461   $260.35   $260.35   $260.30  
  Purchase #6 $71.92   13.802%   $81.8464   $81.85   $81.85   $81.80  
  Purchase #7 $6.61   13.186%   $7.4816   $7.48   $7.50   $7.50  
  7 purchase totals = $702.48       $765.8759   $765.88   $765.95   $765.80