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 $32.25   4.740%   $33.7787   $33.78   $33.80   $33.80  
  Purchase #2 $174.71   12.140%   $195.9198   $195.92   $195.90   $195.90  
  Purchase #3 $220.27   9.127%   $240.374   $240.37   $240.35   $240.40  
  Purchase #4 $214.30   4.600%   $224.1578   $224.16   $224.15   $224.20  
  Purchase #5 $122.31   5.833%   $129.4443   $129.44   $129.45   $129.40  
  Purchase #6 $215.73   8.112%   $233.23   $233.23   $233.25   $233.20  
  Purchase #7 $100.79   6.154%   $106.9926   $106.99   $107.00   $107.00  
  7 purchase totals = $1,080.36       $1,163.8972   $1,163.89   $1,163.90   $1,163.90