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 $89.51   6.175%   $95.0372   $95.04   $95.05   $95.00  
  Purchase #2 $61.80   5.578%   $65.2472   $65.25   $65.25   $65.20  
  Purchase #3 $107.87   8.590%   $117.136   $117.14   $117.15   $117.10  
  Purchase #4 $75.84   13.638%   $86.1831   $86.18   $86.20   $86.20  
  Purchase #5 $183.83   4.506%   $192.1134   $192.11   $192.10   $192.10  
  Purchase #6 $219.50   12.680%   $247.3326   $247.33   $247.35   $247.30  
  Purchase #7 $157.50   6.751%   $168.1328   $168.13   $168.15   $168.10  
  7 purchase totals = $895.85       $971.1823   $971.18   $971.25   $971.00