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 $113.66   11.449%   $126.6729   $126.67   $126.65   $126.70  
  Purchase #2 $112.61   6.775%   $120.2393   $120.24   $120.25   $120.20  
  Purchase #3 $22.48   9.490%   $24.6134   $24.61   $24.60   $24.60  
  Purchase #4 $139.49   3.687%   $144.633   $144.63   $144.65   $144.60  
  Purchase #5 $176.42   9.313%   $192.85   $192.85   $192.85   $192.90  
  Purchase #6 $169.90   8.409%   $184.1869   $184.19   $184.20   $184.20  
  Purchase #7 $191.76   8.253%   $207.586   $207.59   $207.60   $207.60  
  7 purchase totals = $926.32       $1,000.7815   $1,000.78   $1,000.80   $1,000.80