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 $86.84   7.824%   $93.6344   $93.63   $93.65   $93.60  
  Purchase #2 $157.25   5.266%   $165.5308   $165.53   $165.55   $165.50  
  Purchase #3 $154.45   13.765%   $175.71   $175.71   $175.70   $175.70  
  Purchase #4 $216.62   13.492%   $245.8464   $245.85   $245.85   $245.80  
  Purchase #5 $185.62   6.257%   $197.2342   $197.23   $197.25   $197.20  
  Purchase #6 $221.26   13.767%   $251.7209   $251.72   $251.70   $251.70  
  Purchase #7 $163.60   8.789%   $177.9788   $177.98   $178.00   $178.00  
  7 purchase totals = $1,185.64       $1,307.6555   $1,307.65   $1,307.70   $1,307.50