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 $224.57   13.441%   $254.7545   $254.75   $254.75   $254.80  
  Purchase #2 $13.53   11.685%   $15.111   $15.11   $15.10   $15.10  
  Purchase #3 $82.81   3.184%   $85.4467   $85.45   $85.45   $85.40  
  Purchase #4 $155.44   7.152%   $166.5571   $166.56   $166.55   $166.60  
  Purchase #5 $110.33   6.716%   $117.7398   $117.74   $117.75   $117.70  
  Purchase #6 $211.52   4.856%   $221.7914   $221.79   $221.80   $221.80  
  Purchase #7 $119.88   11.379%   $133.5211   $133.52   $133.50   $133.50  
  7 purchase totals = $918.08       $994.9216   $994.92   $994.90   $994.90