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 $240.85   13.853%   $274.215   $274.22   $274.20   $274.20  
  Purchase #2 $194.35   6.122%   $206.2481   $206.25   $206.25   $206.20  
  Purchase #3 $166.91   6.861%   $178.3617   $178.36   $178.35   $178.40  
  Purchase #4 $79.46   5.456%   $83.7953   $83.80   $83.80   $83.80  
  Purchase #5 $243.90   3.312%   $251.978   $251.98   $252.00   $252.00  
  Purchase #6 $209.61   12.653%   $236.132   $236.13   $236.15   $236.10  
  Purchase #7 $62.56   11.326%   $69.6455   $69.65   $69.65   $69.60  
  7 purchase totals = $1,197.64       $1,300.3756   $1,300.39   $1,300.40   $1,300.30