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 $22.77   13.841%   $25.9216   $25.92   $25.90   $25.90  
  Purchase #2 $245.95   12.279%   $276.1502   $276.15   $276.15   $276.20  
  Purchase #3 $93.30   3.233%   $96.3164   $96.32   $96.30   $96.30  
  Purchase #4 $205.52   8.866%   $223.7414   $223.74   $223.75   $223.70  
  Purchase #5 $207.78   3.763%   $215.5988   $215.60   $215.60   $215.60  
  Purchase #6 $250.26   8.300%   $271.0316   $271.03   $271.05   $271.00  
  Purchase #7 $217.52   7.522%   $233.8819   $233.88   $233.90   $233.90  
  7 purchase totals = $1,243.10       $1,342.6419   $1,342.64   $1,342.65   $1,342.60