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 $62.77   4.855%   $65.8175   $65.82   $65.80   $65.80  
  Purchase #2 $106.27   9.443%   $116.3051   $116.31   $116.30   $116.30  
  Purchase #3 $34.85   4.606%   $36.4552   $36.46   $36.45   $36.50  
  Purchase #4 $239.73   7.729%   $258.2587   $258.26   $258.25   $258.30  
  Purchase #5 $96.39   11.217%   $107.2021   $107.20   $107.20   $107.20  
  Purchase #6 $122.91   9.857%   $135.0252   $135.03   $135.05   $135.00  
  Purchase #7 $83.53   7.307%   $89.6335   $89.63   $89.65   $89.60  
  7 purchase totals = $746.45       $808.6973   $808.71   $808.70   $808.70