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 $208.93   8.116%   $225.8868   $225.89   $225.90   $225.90  
  Purchase #2 $115.50   3.270%   $119.2769   $119.28   $119.30   $119.30  
  Purchase #3 $141.84   4.398%   $148.0781   $148.08   $148.10   $148.10  
  Purchase #4 $85.74   7.494%   $92.1654   $92.17   $92.15   $92.20  
  Purchase #5 $204.43   13.726%   $232.4901   $232.49   $232.50   $232.50  
  Purchase #6 $245.95   13.376%   $278.8483   $278.85   $278.85   $278.80  
  Purchase #7 $25.47   3.453%   $26.3495   $26.35   $26.35   $26.30  
  7 purchase totals = $1,027.86       $1,123.0951   $1,123.11   $1,123.15   $1,123.10