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 $246.93   13.211%   $279.5519   $279.55   $279.55   $279.60  
  Purchase #2 $75.66   12.385%   $85.0305   $85.03   $85.05   $85.00  
  Purchase #3 $160.60   8.696%   $174.5658   $174.57   $174.55   $174.60  
  Purchase #4 $162.65   5.401%   $171.4347   $171.43   $171.45   $171.40  
  Purchase #5 $48.87   6.336%   $51.9664   $51.97   $51.95   $52.00  
  Purchase #6 $168.98   10.782%   $187.1994   $187.20   $187.20   $187.20  
  Purchase #7 $86.60   8.778%   $94.2017   $94.20   $94.20   $94.20  
  7 purchase totals = $950.29       $1,043.9504   $1,043.95   $1,043.95   $1,044.00