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 $161.53   13.448%   $183.2526   $183.25   $183.25   $183.30  
  Purchase #2 $57.78   4.464%   $60.3593   $60.36   $60.35   $60.40  
  Purchase #3 $44.58   13.379%   $50.5444   $50.54   $50.55   $50.50  
  Purchase #4 $162.42   6.516%   $173.0033   $173.00   $173.00   $173.00  
  Purchase #5 $121.67   7.365%   $130.631   $130.63   $130.65   $130.60  
  Purchase #6 $211.44   6.579%   $225.3506   $225.35   $225.35   $225.40  
  Purchase #7 $194.48   8.590%   $211.1858   $211.19   $211.20   $211.20  
  7 purchase totals = $953.90       $1,034.3270   $1,034.32   $1,034.35   $1,034.40