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 $76.35   11.706%   $85.2875   $85.29   $85.30   $85.30  
  Purchase #2 $184.48   4.442%   $192.6746   $192.67   $192.65   $192.70  
  Purchase #3 $12.67   10.522%   $14.0031   $14.00   $14.00   $14.00  
  Purchase #4 $79.94   12.705%   $90.0964   $90.10   $90.10   $90.10  
  Purchase #5 $116.34   11.744%   $130.003   $130.00   $130.00   $130.00  
  Purchase #6 $72.27   10.194%   $79.6372   $79.64   $79.65   $79.60  
  Purchase #7 $220.40   9.865%   $242.1425   $242.14   $242.15   $242.10  
  7 purchase totals = $762.45       $833.8443   $833.84   $833.85   $833.80