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 $61.75   11.699%   $68.9741   $68.97   $68.95   $69.00  
  Purchase #2 $25.38   6.177%   $26.9477   $26.95   $26.95   $26.90  
  Purchase #3 $100.67   10.104%   $110.8417   $110.84   $110.85   $110.80  
  Purchase #4 $193.68   6.767%   $206.7863   $206.79   $206.80   $206.80  
  Purchase #5 $6.85   4.578%   $7.1636   $7.16   $7.15   $7.20  
  Purchase #6 $228.53   5.309%   $240.6627   $240.66   $240.65   $240.70  
  Purchase #7 $83.82   5.712%   $88.6078   $88.61   $88.60   $88.60  
  7 purchase totals = $700.68       $749.9839   $749.98   $749.95   $750.00