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 $68.87   11.820%   $77.0104   $77.01   $77.00   $77.00  
  Purchase #2 $197.64   7.239%   $211.9472   $211.95   $211.95   $211.90  
  Purchase #3 $42.95   9.793%   $47.1561   $47.16   $47.15   $47.20  
  Purchase #4 $217.60   11.589%   $242.8177   $242.82   $242.80   $242.80  
  Purchase #5 $163.36   3.709%   $169.419   $169.42   $169.40   $169.40  
  Purchase #6 $179.84   6.783%   $192.0385   $192.04   $192.05   $192.00  
  Purchase #7 $209.83   4.349%   $218.9555   $218.96   $218.95   $219.00  
  7 purchase totals = $1,080.09       $1,159.3444   $1,159.36   $1,159.30   $1,159.30