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 $97.48   3.257%   $100.6549   $100.65   $100.65   $100.70  
  Purchase #2 $67.59   10.561%   $74.7282   $74.73   $74.75   $74.70  
  Purchase #3 $210.76   11.222%   $234.4115   $234.41   $234.40   $234.40  
  Purchase #4 $80.85   5.464%   $85.2676   $85.27   $85.25   $85.30  
  Purchase #5 $197.85   4.337%   $206.4308   $206.43   $206.45   $206.40  
  Purchase #6 $208.47   8.313%   $225.8001   $225.80   $225.80   $225.80  
  Purchase #7 $131.31   7.737%   $141.4695   $141.47   $141.45   $141.50  
  7 purchase totals = $994.31       $1,068.7626   $1,068.76   $1,068.75   $1,068.80