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 $250.39   12.685%   $282.152   $282.15   $282.15   $282.20  
  Purchase #2 $63.66   4.578%   $66.5744   $66.57   $66.55   $66.60  
  Purchase #3 $43.45   12.498%   $48.8804   $48.88   $48.90   $48.90  
  Purchase #4 $209.42   5.208%   $220.3266   $220.33   $220.35   $220.30  
  Purchase #5 $133.82   7.432%   $143.7655   $143.77   $143.75   $143.80  
  Purchase #6 $150.47   9.285%   $164.4411   $164.44   $164.45   $164.40  
  Purchase #7 $135.62   5.275%   $142.774   $142.77   $142.75   $142.80  
  7 purchase totals = $986.83       $1,068.9140   $1,068.91   $1,068.90   $1,069.00