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 $127.76   11.304%   $142.202   $142.20   $142.20   $142.20  
  Purchase #2 $60.94   4.587%   $63.7353   $63.74   $63.75   $63.70  
  Purchase #3 $162.39   10.479%   $179.4068   $179.41   $179.40   $179.40  
  Purchase #4 $36.32   11.809%   $40.609   $40.61   $40.60   $40.60  
  Purchase #5 $205.89   5.414%   $217.0369   $217.04   $217.05   $217.00  
  Purchase #6 $190.80   10.451%   $210.7405   $210.74   $210.75   $210.70  
  Purchase #7 $166.47   7.320%   $178.6556   $178.66   $178.65   $178.70  
  7 purchase totals = $950.57       $1,032.3861   $1,032.40   $1,032.40   $1,032.30