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 $94.78   9.582%   $103.8618   $103.86   $103.85   $103.90  
  Purchase #2 $162.71   4.713%   $170.3785   $170.38   $170.40   $170.40  
  Purchase #3 $220.76   10.577%   $244.1098   $244.11   $244.10   $244.10  
  Purchase #4 $201.49   8.118%   $217.847   $217.85   $217.85   $217.80  
  Purchase #5 $64.36   9.788%   $70.6596   $70.66   $70.65   $70.70  
  Purchase #6 $177.36   13.465%   $201.2415   $201.24   $201.25   $201.20  
  Purchase #7 $171.56   13.159%   $194.1356   $194.14   $194.15   $194.10  
  7 purchase totals = $1,093.02       $1,202.2338   $1,202.24   $1,202.25   $1,202.20