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 $63.44   6.591%   $67.6213   $67.62   $67.60   $67.60  
  Purchase #2 $163.95   13.452%   $186.0046   $186.00   $186.00   $186.00  
  Purchase #3 $49.36   9.574%   $54.0857   $54.09   $54.10   $54.10  
  Purchase #4 $137.64   10.297%   $151.8128   $151.81   $151.80   $151.80  
  Purchase #5 $91.86   7.727%   $98.958   $98.96   $98.95   $99.00  
  Purchase #6 $7.80   12.736%   $8.7934   $8.79   $8.80   $8.80  
  Purchase #7 $197.75   4.150%   $205.9566   $205.96   $205.95   $206.00  
  7 purchase totals = $711.80       $773.2324   $773.23   $773.20   $773.30