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 $73.58   11.391%   $81.9615   $81.96   $81.95   $82.00  
  Purchase #2 $208.28   6.417%   $221.6453   $221.65   $221.65   $221.60  
  Purchase #3 $246.88   10.323%   $272.3654   $272.37   $272.35   $272.40  
  Purchase #4 $226.81   3.564%   $234.8935   $234.89   $234.90   $234.90  
  Purchase #5 $93.42   3.839%   $97.0064   $97.01   $97.00   $97.00  
  Purchase #6 $99.31   4.490%   $103.769   $103.77   $103.75   $103.80  
  Purchase #7 $92.74   9.142%   $101.2183   $101.22   $101.20   $101.20  
  7 purchase totals = $1,041.02       $1,112.8594   $1,112.87   $1,112.80   $1,112.90