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 $244.43   13.571%   $277.6016   $277.60   $277.60   $277.60  
  Purchase #2 $93.76   11.280%   $104.3361   $104.34   $104.35   $104.30  
  Purchase #3 $183.74   4.434%   $191.887   $191.89   $191.90   $191.90  
  Purchase #4 $114.91   8.578%   $124.767   $124.77   $124.75   $124.80  
  Purchase #5 $195.95   11.703%   $218.882   $218.88   $218.90   $218.90  
  Purchase #6 $86.56   13.561%   $98.2984   $98.30   $98.30   $98.30  
  Purchase #7 $139.31   10.445%   $153.8609   $153.86   $153.85   $153.90  
  7 purchase totals = $1,058.66       $1,169.6330   $1,169.64   $1,169.65   $1,169.70