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 $122.58   3.233%   $126.543   $126.54   $126.55   $126.50  
  Purchase #2 $49.96   7.593%   $53.7535   $53.75   $53.75   $53.80  
  Purchase #3 $126.25   3.723%   $130.9503   $130.95   $130.95   $131.00  
  Purchase #4 $238.70   10.357%   $263.4222   $263.42   $263.40   $263.40  
  Purchase #5 $202.37   7.264%   $217.0702   $217.07   $217.05   $217.10  
  Purchase #6 $202.50   11.501%   $225.7895   $225.79   $225.80   $225.80  
  Purchase #7 $204.81   9.282%   $223.8205   $223.82   $223.80   $223.80  
  7 purchase totals = $1,147.17       $1,241.3492   $1,241.34   $1,241.30   $1,241.40