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 $244.95   5.862%   $259.309   $259.31   $259.30   $259.30  
  Purchase #2 $97.34   10.305%   $107.3709   $107.37   $107.35   $107.40  
  Purchase #3 $194.47   4.454%   $203.1317   $203.13   $203.15   $203.10  
  Purchase #4 $72.89   5.779%   $77.1023   $77.10   $77.10   $77.10  
  Purchase #5 $189.67   13.152%   $214.6154   $214.62   $214.60   $214.60  
  Purchase #6 $37.76   11.544%   $42.119   $42.12   $42.10   $42.10  
  Purchase #7 $105.93   7.325%   $113.6894   $113.69   $113.70   $113.70  
  7 purchase totals = $943.01       $1,017.3377   $1,017.34   $1,017.30   $1,017.30