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 $64.32   8.214%   $69.6032   $69.60   $69.60   $69.60  
  Purchase #2 $192.31   4.674%   $201.2986   $201.30   $201.30   $201.30  
  Purchase #3 $80.68   3.768%   $83.72   $83.72   $83.70   $83.70  
  Purchase #4 $53.44   4.406%   $55.7946   $55.79   $55.80   $55.80  
  Purchase #5 $245.48   4.841%   $257.3637   $257.36   $257.35   $257.40  
  Purchase #6 $144.84   10.608%   $160.2046   $160.20   $160.20   $160.20  
  Purchase #7 $115.62   12.217%   $129.7453   $129.75   $129.75   $129.70  
  7 purchase totals = $896.69       $957.7300   $957.72   $957.70   $957.70