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 $169.65   8.661%   $184.3434   $184.34   $184.35   $184.30  
  Purchase #2 $54.64   10.268%   $60.2504   $60.25   $60.25   $60.30  
  Purchase #3 $229.51   4.500%   $239.838   $239.84   $239.85   $239.80  
  Purchase #4 $159.91   7.325%   $171.6234   $171.62   $171.60   $171.60  
  Purchase #5 $131.54   7.311%   $141.1569   $141.16   $141.15   $141.20  
  Purchase #6 $217.36   4.399%   $226.9217   $226.92   $226.90   $226.90  
  Purchase #7 $92.47   4.519%   $96.6487   $96.65   $96.65   $96.60  
  7 purchase totals = $1,055.08       $1,120.7825   $1,120.78   $1,120.75   $1,120.70