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 $85.94   12.555%   $96.7298   $96.73   $96.75   $96.70  
  Purchase #2 $206.83   5.706%   $218.6317   $218.63   $218.65   $218.60  
  Purchase #3 $150.60   13.677%   $171.1976   $171.20   $171.20   $171.20  
  Purchase #4 $184.67   6.769%   $197.1703   $197.17   $197.15   $197.20  
  Purchase #5 $22.28   12.150%   $24.987   $24.99   $25.00   $25.00  
  Purchase #6 $186.26   3.709%   $193.1684   $193.17   $193.15   $193.20  
  Purchase #7 $9.31   8.398%   $10.0919   $10.09   $10.10   $10.10  
  7 purchase totals = $845.89       $911.9767   $911.98   $912.00   $912.00