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 $203.72   11.118%   $226.3696   $226.37   $226.35   $226.40  
  Purchase #2 $108.43   5.165%   $114.0304   $114.03   $114.05   $114.00  
  Purchase #3 $64.80   7.445%   $69.6244   $69.62   $69.60   $69.60  
  Purchase #4 $74.29   3.195%   $76.6636   $76.66   $76.65   $76.70  
  Purchase #5 $87.30   10.195%   $96.2002   $96.20   $96.20   $96.20  
  Purchase #6 $249.59   10.488%   $275.767   $275.77   $275.75   $275.80  
  Purchase #7 $150.71   9.281%   $164.6974   $164.70   $164.70   $164.70  
  7 purchase totals = $938.84       $1,023.3526   $1,023.35   $1,023.30   $1,023.40