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 $57.97   9.316%   $63.3705   $63.37   $63.35   $63.40  
  Purchase #2 $240.28   5.153%   $252.6616   $252.66   $252.65   $252.70  
  Purchase #3 $134.62   12.672%   $151.679   $151.68   $151.70   $151.70  
  Purchase #4 $82.74   9.733%   $90.7931   $90.79   $90.80   $90.80  
  Purchase #5 $11.31   6.421%   $12.0362   $12.04   $12.05   $12.00  
  Purchase #6 $150.96   5.648%   $159.4862   $159.49   $159.50   $159.50  
  Purchase #7 $32.30   13.643%   $36.7067   $36.71   $36.70   $36.70  
  7 purchase totals = $710.18       $766.7333   $766.74   $766.75   $766.80