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 $48.77   8.307%   $52.8213   $52.82   $52.80   $52.80  
  Purchase #2 $151.33   7.249%   $162.2999   $162.30   $162.30   $162.30  
  Purchase #3 $83.68   3.808%   $86.8665   $86.87   $86.85   $86.90  
  Purchase #4 $239.58   10.736%   $265.3013   $265.30   $265.30   $265.30  
  Purchase #5 $153.51   13.655%   $174.4718   $174.47   $174.45   $174.50  
  Purchase #6 $185.82   9.723%   $203.8873   $203.89   $203.90   $203.90  
  Purchase #7 $205.33   13.528%   $233.107   $233.11   $233.10   $233.10  
  7 purchase totals = $1,068.02       $1,178.7551   $1,178.76   $1,178.70   $1,178.80