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 $115.44   9.374%   $126.2613   $126.26   $126.25   $126.30  
  Purchase #2 $233.35   13.632%   $265.1603   $265.16   $265.15   $265.20  
  Purchase #3 $96.75   3.571%   $100.2049   $100.20   $100.20   $100.20  
  Purchase #4 $104.29   3.873%   $108.3292   $108.33   $108.35   $108.30  
  Purchase #5 $221.52   3.196%   $228.5998   $228.60   $228.60   $228.60  
  Purchase #6 $222.77   12.653%   $250.9571   $250.96   $250.95   $251.00  
  Purchase #7 $118.43   13.251%   $134.1232   $134.12   $134.10   $134.10  
  7 purchase totals = $1,112.55       $1,213.6358   $1,213.63   $1,213.60   $1,213.70