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 $117.47   7.766%   $126.5927   $126.59   $126.60   $126.60  
  Purchase #2 $86.35   13.531%   $98.034   $98.03   $98.05   $98.00  
  Purchase #3 $51.28   10.157%   $56.4885   $56.49   $56.50   $56.50  
  Purchase #4 $237.28   6.105%   $251.7659   $251.77   $251.75   $251.80  
  Purchase #5 $101.49   4.693%   $106.2529   $106.25   $106.25   $106.30  
  Purchase #6 $216.67   7.621%   $233.1824   $233.18   $233.20   $233.20  
  Purchase #7 $115.58   10.764%   $128.021   $128.02   $128.00   $128.00  
  7 purchase totals = $926.12       $1,000.3374   $1,000.33   $1,000.35   $1,000.40