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 $95.39   8.331%   $103.3369   $103.34   $103.35   $103.30  
  Purchase #2 $114.65   6.603%   $122.2203   $122.22   $122.20   $122.20  
  Purchase #3 $162.91   5.375%   $171.6664   $171.67   $171.65   $171.70  
  Purchase #4 $118.89   8.590%   $129.1027   $129.10   $129.10   $129.10  
  Purchase #5 $75.61   8.512%   $82.0459   $82.05   $82.05   $82.00  
  Purchase #6 $68.92   8.481%   $74.7651   $74.77   $74.75   $74.80  
  Purchase #7 $107.91   7.771%   $116.2957   $116.30   $116.30   $116.30  
  7 purchase totals = $744.28       $799.4330   $799.45   $799.40   $799.40