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 $168.86   8.850%   $183.8041   $183.80   $183.80   $183.80  
  Purchase #2 $213.51   8.765%   $232.2242   $232.22   $232.20   $232.20  
  Purchase #3 $20.93   9.538%   $22.9263   $22.93   $22.95   $22.90  
  Purchase #4 $162.89   7.725%   $175.4733   $175.47   $175.45   $175.50  
  Purchase #5 $230.97   5.835%   $244.4471   $244.45   $244.45   $244.40  
  Purchase #6 $125.51   9.527%   $137.4673   $137.47   $137.45   $137.50  
  Purchase #7 $95.78   8.268%   $103.6991   $103.70   $103.70   $103.70  
  7 purchase totals = $1,018.45       $1,100.0414   $1,100.04   $1,100.00   $1,100.00