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 $96.54   5.651%   $101.9955   $102.00   $102.00   $102.00  
  Purchase #2 $73.99   4.539%   $77.3484   $77.35   $77.35   $77.30  
  Purchase #3 $192.97   5.383%   $203.3576   $203.36   $203.35   $203.40  
  Purchase #4 $96.92   10.708%   $107.2982   $107.30   $107.30   $107.30  
  Purchase #5 $20.70   5.727%   $21.8855   $21.89   $21.90   $21.90  
  Purchase #6 $64.85   5.296%   $68.2845   $68.28   $68.30   $68.30  
  Purchase #7 $238.45   6.827%   $254.729   $254.73   $254.75   $254.70  
  7 purchase totals = $784.42       $834.8987   $834.91   $834.95   $834.90