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 $244.67   9.827%   $268.7137   $268.71   $268.70   $268.70  
  Purchase #2 $180.68   11.696%   $201.8123   $201.81   $201.80   $201.80  
  Purchase #3 $249.69   8.844%   $271.7726   $271.77   $271.75   $271.80  
  Purchase #4 $81.46   4.765%   $85.3416   $85.34   $85.35   $85.30  
  Purchase #5 $231.48   9.129%   $252.6118   $252.61   $252.60   $252.60  
  Purchase #6 $191.77   7.750%   $206.6322   $206.63   $206.65   $206.60  
  Purchase #7 $96.70   9.808%   $106.1843   $106.18   $106.20   $106.20  
  7 purchase totals = $1,276.45       $1,393.0685   $1,393.05   $1,393.05   $1,393.00