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 $198.55   12.486%   $223.341   $223.34   $223.35   $223.30  
  Purchase #2 $51.94   6.147%   $55.1328   $55.13   $55.15   $55.10  
  Purchase #3 $161.30   4.814%   $169.065   $169.07   $169.05   $169.10  
  Purchase #4 $35.49   6.185%   $37.6851   $37.69   $37.70   $37.70  
  Purchase #5 $152.40   7.498%   $163.827   $163.83   $163.85   $163.80  
  Purchase #6 $147.81   3.852%   $153.5036   $153.50   $153.50   $153.50  
  Purchase #7 $61.41   4.141%   $63.953   $63.95   $63.95   $64.00  
  7 purchase totals = $808.90       $866.5075   $866.51   $866.55   $866.50