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 $192.54   5.826%   $203.7574   $203.76   $203.75   $203.80  
  Purchase #2 $212.84   13.314%   $241.1775   $241.18   $241.20   $241.20  
  Purchase #3 $220.30   13.601%   $250.263   $250.26   $250.25   $250.30  
  Purchase #4 $83.70   8.857%   $91.1133   $91.11   $91.10   $91.10  
  Purchase #5 $36.65   3.778%   $38.0346   $38.03   $38.05   $38.00  
  Purchase #6 $236.82   12.306%   $265.9631   $265.96   $265.95   $266.00  
  Purchase #7 $190.49   13.297%   $215.8195   $215.82   $215.80   $215.80  
  7 purchase totals = $1,173.34       $1,306.1284   $1,306.12   $1,306.10   $1,306.20