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 $60.88   7.743%   $65.5939   $65.59   $65.60   $65.60  
  Purchase #2 $129.97   10.550%   $143.6818   $143.68   $143.70   $143.70  
  Purchase #3 $171.92   13.538%   $195.1945   $195.19   $195.20   $195.20  
  Purchase #4 $223.50   8.111%   $241.6281   $241.63   $241.65   $241.60  
  Purchase #5 $239.80   7.829%   $258.5739   $258.57   $258.55   $258.60  
  Purchase #6 $163.40   10.800%   $181.0472   $181.05   $181.05   $181.00  
  Purchase #7 $25.76   3.673%   $26.7062   $26.71   $26.70   $26.70  
  7 purchase totals = $1,015.23       $1,112.4256   $1,112.42   $1,112.45   $1,112.40