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 $224.98   13.258%   $254.8078   $254.81   $254.80   $254.80  
  Purchase #2 $243.38   3.804%   $252.6382   $252.64   $252.65   $252.60  
  Purchase #3 $202.75   9.365%   $221.7375   $221.74   $221.75   $221.70  
  Purchase #4 $140.91   9.238%   $153.9273   $153.93   $153.95   $153.90  
  Purchase #5 $159.89   10.832%   $177.2093   $177.21   $177.20   $177.20  
  Purchase #6 $135.91   13.490%   $154.2443   $154.24   $154.25   $154.20  
  Purchase #7 $33.34   8.672%   $36.2312   $36.23   $36.25   $36.20  
  7 purchase totals = $1,141.16       $1,250.7956   $1,250.80   $1,250.85   $1,250.60