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 $168.34   9.343%   $184.068   $184.07   $184.05   $184.10  
  Purchase #2 $246.92   7.566%   $265.602   $265.60   $265.60   $265.60  
  Purchase #3 $198.98   3.445%   $205.8349   $205.83   $205.85   $205.80  
  Purchase #4 $196.52   8.467%   $213.1593   $213.16   $213.15   $213.20  
  Purchase #5 $209.94   11.584%   $234.2594   $234.26   $234.25   $234.30  
  Purchase #6 $202.63   6.789%   $216.3866   $216.39   $216.40   $216.40  
  Purchase #7 $198.97   7.632%   $214.1554   $214.16   $214.15   $214.20  
  7 purchase totals = $1,422.30       $1,533.4656   $1,533.47   $1,533.45   $1,533.60