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 $192.91   6.582%   $205.6073   $205.61   $205.60   $205.60  
  Purchase #2 $139.99   7.131%   $149.9727   $149.97   $149.95   $150.00  
  Purchase #3 $111.93   11.716%   $125.0437   $125.04   $125.05   $125.00  
  Purchase #4 $188.72   12.825%   $212.9233   $212.92   $212.90   $212.90  
  Purchase #5 $52.47   4.637%   $54.903   $54.90   $54.90   $54.90  
  Purchase #6 $64.42   7.421%   $69.2006   $69.20   $69.20   $69.20  
  Purchase #7 $170.92   8.607%   $185.6311   $185.63   $185.65   $185.60  
  7 purchase totals = $921.36       $1,003.2817   $1,003.27   $1,003.25   $1,003.20