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 $89.47   6.869%   $95.6157   $95.62   $95.60   $95.60  
  Purchase #2 $52.48   12.787%   $59.1906   $59.19   $59.20   $59.20  
  Purchase #3 $131.45   12.419%   $147.7748   $147.77   $147.75   $147.80  
  Purchase #4 $12.80   5.186%   $13.4638   $13.46   $13.45   $13.50  
  Purchase #5 $91.54   4.518%   $95.6758   $95.68   $95.70   $95.70  
  Purchase #6 $202.55   10.226%   $223.2628   $223.26   $223.25   $223.30  
  Purchase #7 $126.84   5.515%   $133.8352   $133.84   $133.85   $133.80  
  7 purchase totals = $707.13       $768.8187   $768.82   $768.80   $768.90