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 $87.62   12.573%   $98.6365   $98.64   $98.65   $98.60  
  Purchase #2 $230.86   8.415%   $250.2869   $250.29   $250.30   $250.30  
  Purchase #3 $194.34   9.278%   $212.3709   $212.37   $212.35   $212.40  
  Purchase #4 $176.25   3.686%   $182.7466   $182.75   $182.75   $182.70  
  Purchase #5 $183.29   13.517%   $208.0653   $208.07   $208.05   $208.10  
  Purchase #6 $70.49   13.417%   $79.9476   $79.95   $79.95   $79.90  
  Purchase #7 $183.27   9.145%   $200.03   $200.03   $200.05   $200.00  
  7 purchase totals = $1,126.12       $1,232.0838   $1,232.10   $1,232.10   $1,232.00