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 $64.44   8.281%   $69.7763   $69.78   $69.80   $69.80  
  Purchase #2 $96.62   12.214%   $108.4212   $108.42   $108.40   $108.40  
  Purchase #3 $239.75   11.201%   $266.6044   $266.60   $266.60   $266.60  
  Purchase #4 $232.27   8.776%   $252.654   $252.65   $252.65   $252.70  
  Purchase #5 $212.38   9.405%   $232.3543   $232.35   $232.35   $232.40  
  Purchase #6 $64.29   11.414%   $71.6281   $71.63   $71.65   $71.60  
  Purchase #7 $24.60   8.656%   $26.7294   $26.73   $26.75   $26.70  
  7 purchase totals = $934.35       $1,028.1677   $1,028.16   $1,028.20   $1,028.20