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 $208.62   11.403%   $232.4089   $232.41   $232.40   $232.40  
  Purchase #2 $153.43   6.389%   $163.2326   $163.23   $163.25   $163.20  
  Purchase #3 $18.48   8.448%   $20.0412   $20.04   $20.05   $20.00  
  Purchase #4 $162.39   11.806%   $181.5618   $181.56   $181.55   $181.60  
  Purchase #5 $247.72   13.708%   $281.6775   $281.68   $281.70   $281.70  
  Purchase #6 $74.35   7.129%   $79.6504   $79.65   $79.65   $79.70  
  Purchase #7 $191.62   5.493%   $202.1457   $202.15   $202.15   $202.10  
  7 purchase totals = $1,056.61       $1,160.7181   $1,160.72   $1,160.75   $1,160.70