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 $242.62   4.516%   $253.5767   $253.58   $253.60   $253.60  
  Purchase #2 $153.30   3.864%   $159.2235   $159.22   $159.20   $159.20  
  Purchase #3 $112.88   10.662%   $124.9153   $124.92   $124.90   $124.90  
  Purchase #4 $86.92   9.550%   $95.2209   $95.22   $95.20   $95.20  
  Purchase #5 $97.49   13.449%   $110.6014   $110.60   $110.60   $110.60  
  Purchase #6 $198.95   3.676%   $206.2634   $206.26   $206.25   $206.30  
  Purchase #7 $228.70   9.601%   $250.6575   $250.66   $250.65   $250.70  
  7 purchase totals = $1,120.86       $1,200.4587   $1,200.46   $1,200.40   $1,200.50