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 $60.77   8.327%   $65.8303   $65.83   $65.85   $65.80  
  Purchase #2 $135.52   4.345%   $141.4083   $141.41   $141.40   $141.40  
  Purchase #3 $185.62   10.451%   $205.0191   $205.02   $205.00   $205.00  
  Purchase #4 $172.56   11.530%   $192.4562   $192.46   $192.45   $192.50  
  Purchase #5 $90.60   6.747%   $96.7128   $96.71   $96.70   $96.70  
  Purchase #6 $126.66   4.218%   $132.0025   $132.00   $132.00   $132.00  
  Purchase #7 $43.30   12.269%   $48.6125   $48.61   $48.60   $48.60  
  7 purchase totals = $815.03       $882.0417   $882.04   $882.00   $882.00