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 $242.42   8.815%   $263.7893   $263.79   $263.80   $263.80  
  Purchase #2 $132.41   7.494%   $142.3328   $142.33   $142.35   $142.30  
  Purchase #3 $202.79   9.329%   $221.7083   $221.71   $221.70   $221.70  
  Purchase #4 $49.86   13.521%   $56.6016   $56.60   $56.60   $56.60  
  Purchase #5 $238.49   12.172%   $267.519   $267.52   $267.50   $267.50  
  Purchase #6 $73.63   12.849%   $83.0907   $83.09   $83.10   $83.10  
  Purchase #7 $151.33   12.328%   $169.986   $169.99   $170.00   $170.00  
  7 purchase totals = $1,090.93       $1,205.0277   $1,205.03   $1,205.05   $1,205.00