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 $24.97   6.664%   $26.634   $26.63   $26.65   $26.60  
  Purchase #2 $75.98   4.762%   $79.5982   $79.60   $79.60   $79.60  
  Purchase #3 $84.72   6.275%   $90.0362   $90.04   $90.05   $90.00  
  Purchase #4 $36.82   12.618%   $41.4659   $41.47   $41.45   $41.50  
  Purchase #5 $225.82   8.205%   $244.3485   $244.35   $244.35   $244.30  
  Purchase #6 $203.48   8.108%   $219.9782   $219.98   $220.00   $220.00  
  Purchase #7 $84.80   8.135%   $91.6985   $91.70   $91.70   $91.70  
  7 purchase totals = $736.59       $793.7595   $793.77   $793.80   $793.70