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 $171.44   9.451%   $187.6428   $187.64   $187.65   $187.60  
  Purchase #2 $23.51   13.321%   $26.6418   $26.64   $26.65   $26.60  
  Purchase #3 $200.66   13.806%   $228.3631   $228.36   $228.35   $228.40  
  Purchase #4 $212.47   13.130%   $240.3673   $240.37   $240.35   $240.40  
  Purchase #5 $76.88   12.108%   $86.1886   $86.19   $86.20   $86.20  
  Purchase #6 $196.78   13.851%   $224.036   $224.04   $224.05   $224.00  
  Purchase #7 $247.90   11.454%   $276.2945   $276.29   $276.30   $276.30  
  7 purchase totals = $1,129.64       $1,269.5341   $1,269.53   $1,269.55   $1,269.50