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 $178.85   7.485%   $192.2369   $192.24   $192.25   $192.20  
  Purchase #2 $92.97   11.459%   $103.6234   $103.62   $103.60   $103.60  
  Purchase #3 $26.97   6.311%   $28.6721   $28.67   $28.65   $28.70  
  Purchase #4 $59.37   7.265%   $63.6832   $63.68   $63.70   $63.70  
  Purchase #5 $161.26   10.532%   $178.2439   $178.24   $178.25   $178.20  
  Purchase #6 $50.98   6.695%   $54.3931   $54.39   $54.40   $54.40  
  Purchase #7 $200.87   5.281%   $211.4779   $211.48   $211.50   $211.50  
  7 purchase totals = $771.27       $832.3305   $832.32   $832.35   $832.30