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 $96.87   9.582%   $106.1521   $106.15   $106.15   $106.20  
  Purchase #2 $215.87   12.315%   $242.4544   $242.45   $242.45   $242.50  
  Purchase #3 $236.47   13.647%   $268.7411   $268.74   $268.75   $268.70  
  Purchase #4 $149.69   11.461%   $166.846   $166.85   $166.85   $166.80  
  Purchase #5 $178.46   7.486%   $191.8195   $191.82   $191.80   $191.80  
  Purchase #6 $108.51   6.346%   $115.396   $115.40   $115.40   $115.40  
  Purchase #7 $119.32   3.651%   $123.6764   $123.68   $123.70   $123.70  
  7 purchase totals = $1,105.19       $1,215.0855   $1,215.09   $1,215.10   $1,215.10