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 $58.75   6.840%   $62.7685   $62.77   $62.75   $62.80  
  Purchase #2 $79.43   4.204%   $82.7692   $82.77   $82.75   $82.80  
  Purchase #3 $189.80   9.238%   $207.3337   $207.33   $207.35   $207.30  
  Purchase #4 $58.43   12.801%   $65.9096   $65.91   $65.90   $65.90  
  Purchase #5 $155.68   9.510%   $170.4852   $170.49   $170.50   $170.50  
  Purchase #6 $184.93   11.125%   $205.5035   $205.50   $205.50   $205.50  
  Purchase #7 $208.76   8.657%   $226.8324   $226.83   $226.85   $226.80  
  7 purchase totals = $935.78       $1,021.6021   $1,021.60   $1,021.60   $1,021.60