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 $206.91   13.626%   $235.1036   $235.10   $235.10   $235.10  
  Purchase #2 $100.59   6.399%   $107.0268   $107.03   $107.05   $107.00  
  Purchase #3 $152.94   5.564%   $161.4496   $161.45   $161.45   $161.40  
  Purchase #4 $59.63   4.405%   $62.2567   $62.26   $62.25   $62.30  
  Purchase #5 $160.82   6.535%   $171.3296   $171.33   $171.35   $171.30  
  Purchase #6 $176.70   11.674%   $197.328   $197.33   $197.35   $197.30  
  Purchase #7 $241.47   9.742%   $264.994   $264.99   $265.00   $265.00  
  7 purchase totals = $1,099.06       $1,199.4883   $1,199.49   $1,199.55   $1,199.40