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 $97.72   5.373%   $102.9705   $102.97   $102.95   $103.00  
  Purchase #2 $242.31   8.785%   $263.5969   $263.60   $263.60   $263.60  
  Purchase #3 $14.29   11.395%   $15.9183   $15.92   $15.90   $15.90  
  Purchase #4 $46.60   8.534%   $50.5768   $50.58   $50.60   $50.60  
  Purchase #5 $153.86   6.766%   $164.2702   $164.27   $164.25   $164.30  
  Purchase #6 $87.66   12.516%   $98.6315   $98.63   $98.65   $98.60  
  Purchase #7 $37.33   4.561%   $39.0326   $39.03   $39.05   $39.00  
  7 purchase totals = $679.77       $734.9968   $735.00   $735.00   $735.00