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 $118.83   13.618%   $135.0123   $135.01   $135.00   $135.00  
  Purchase #2 $237.29   3.299%   $245.1182   $245.12   $245.10   $245.10  
  Purchase #3 $74.78   7.569%   $80.4401   $80.44   $80.45   $80.40  
  Purchase #4 $200.68   10.435%   $221.621   $221.62   $221.60   $221.60  
  Purchase #5 $202.63   3.758%   $210.2448   $210.24   $210.25   $210.20  
  Purchase #6 $177.35   13.211%   $200.7797   $200.78   $200.80   $200.80  
  Purchase #7 $247.42   10.762%   $274.0473   $274.05   $274.05   $274.00  
  7 purchase totals = $1,258.98       $1,367.2634   $1,367.26   $1,367.25   $1,367.10