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 $196.72   13.616%   $223.5054   $223.51   $223.50   $223.50  
  Purchase #2 $125.48   12.770%   $141.5038   $141.50   $141.50   $141.50  
  Purchase #3 $74.67   10.441%   $82.4663   $82.47   $82.45   $82.50  
  Purchase #4 $195.47   8.752%   $212.5775   $212.58   $212.60   $212.60  
  Purchase #5 $222.50   4.689%   $232.933   $232.93   $232.95   $232.90  
  Purchase #6 $193.73   6.834%   $206.9695   $206.97   $206.95   $207.00  
  Purchase #7 $243.71   4.257%   $254.0847   $254.08   $254.10   $254.10  
  7 purchase totals = $1,252.28       $1,354.0402   $1,354.04   $1,354.05   $1,354.10