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 $95.64   3.471%   $98.9597   $98.96   $98.95   $99.00  
  Purchase #2 $96.84   13.529%   $109.9415   $109.94   $109.95   $109.90  
  Purchase #3 $114.75   4.271%   $119.651   $119.65   $119.65   $119.70  
  Purchase #4 $79.37   5.736%   $83.9227   $83.92   $83.90   $83.90  
  Purchase #5 $242.94   3.689%   $251.9021   $251.90   $251.90   $251.90  
  Purchase #6 $207.46   12.110%   $232.5834   $232.58   $232.60   $232.60  
  Purchase #7 $136.36   8.695%   $148.2165   $148.22   $148.20   $148.20  
  7 purchase totals = $973.36       $1,045.1769   $1,045.17   $1,045.15   $1,045.20