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 $104.60   13.427%   $118.6446   $118.64   $118.65   $118.60  
  Purchase #2 $215.34   11.420%   $239.9318   $239.93   $239.95   $239.90  
  Purchase #3 $65.92   6.304%   $70.0756   $70.08   $70.10   $70.10  
  Purchase #4 $148.79   13.841%   $169.384   $169.38   $169.40   $169.40  
  Purchase #5 $104.81   12.542%   $117.9553   $117.96   $117.95   $118.00  
  Purchase #6 $157.37   9.137%   $171.7489   $171.75   $171.75   $171.70  
  Purchase #7 $124.65   5.525%   $131.5369   $131.54   $131.55   $131.50  
  7 purchase totals = $921.48       $1,019.2771   $1,019.28   $1,019.35   $1,019.20