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 $159.51   3.757%   $165.5028   $165.50   $165.50   $165.50  
  Purchase #2 $150.68   6.648%   $160.6972   $160.70   $160.70   $160.70  
  Purchase #3 $42.31   5.618%   $44.687   $44.69   $44.70   $44.70  
  Purchase #4 $183.93   13.518%   $208.7937   $208.79   $208.80   $208.80  
  Purchase #5 $240.69   9.742%   $264.138   $264.14   $264.15   $264.10  
  Purchase #6 $244.48   10.607%   $270.412   $270.41   $270.40   $270.40  
  Purchase #7 $156.81   3.632%   $162.5053   $162.51   $162.50   $162.50  
  7 purchase totals = $1,178.41       $1,276.7360   $1,276.74   $1,276.75   $1,276.70