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 $117.62   6.529%   $125.2994   $125.30   $125.30   $125.30  
  Purchase #2 $248.52   10.502%   $274.6196   $274.62   $274.60   $274.60  
  Purchase #3 $95.74   5.538%   $101.0421   $101.04   $101.05   $101.00  
  Purchase #4 $62.31   3.163%   $64.2809   $64.28   $64.30   $64.30  
  Purchase #5 $25.70   3.866%   $26.6936   $26.69   $26.70   $26.70  
  Purchase #6 $240.36   3.217%   $248.0924   $248.09   $248.10   $248.10  
  Purchase #7 $175.93   7.409%   $188.9647   $188.96   $188.95   $189.00  
  7 purchase totals = $966.18       $1,028.9927   $1,028.98   $1,029.00   $1,029.00