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 $151.69   8.594%   $164.7262   $164.73   $164.75   $164.70  
  Purchase #2 $107.84   7.525%   $115.955   $115.96   $115.95   $116.00  
  Purchase #3 $85.30   12.782%   $96.203   $96.20   $96.20   $96.20  
  Purchase #4 $112.64   13.268%   $127.5851   $127.59   $127.60   $127.60  
  Purchase #5 $27.46   7.758%   $29.5903   $29.59   $29.60   $29.60  
  Purchase #6 $248.71   11.506%   $277.3266   $277.33   $277.35   $277.30  
  Purchase #7 $103.82   8.829%   $112.9863   $112.99   $113.00   $113.00  
  7 purchase totals = $837.46       $924.3725   $924.39   $924.45   $924.40