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 $193.99   12.692%   $218.6112   $218.61   $218.60   $218.60  
  Purchase #2 $220.79   7.702%   $237.7952   $237.80   $237.80   $237.80  
  Purchase #3 $24.44   10.240%   $26.9427   $26.94   $26.95   $26.90  
  Purchase #4 $76.43   3.670%   $79.235   $79.24   $79.25   $79.20  
  Purchase #5 $65.87   13.821%   $74.9739   $74.97   $74.95   $75.00  
  Purchase #6 $162.61   8.399%   $176.2676   $176.27   $176.25   $176.30  
  Purchase #7 $187.47   11.232%   $208.5266   $208.53   $208.55   $208.50  
  7 purchase totals = $931.60       $1,022.3522   $1,022.36   $1,022.35   $1,022.30