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 $197.44   8.281%   $213.79   $213.79   $213.80   $213.80  
  Purchase #2 $84.34   5.538%   $89.0107   $89.01   $89.00   $89.00  
  Purchase #3 $18.86   9.429%   $20.6383   $20.64   $20.65   $20.60  
  Purchase #4 $210.54   5.812%   $222.7766   $222.78   $222.80   $222.80  
  Purchase #5 $187.69   3.262%   $193.8124   $193.81   $193.80   $193.80  
  Purchase #6 $23.50   9.783%   $25.799   $25.80   $25.80   $25.80  
  Purchase #7 $67.69   10.762%   $74.9748   $74.97   $74.95   $75.00  
  7 purchase totals = $790.06       $840.8018   $840.80   $840.80   $840.80