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 $224.32   13.301%   $254.1568   $254.16   $254.15   $254.20  
  Purchase #2 $163.86   10.360%   $180.8359   $180.84   $180.85   $180.80  
  Purchase #3 $85.40   9.587%   $93.5873   $93.59   $93.60   $93.60  
  Purchase #4 $71.50   13.262%   $80.9823   $80.98   $81.00   $81.00  
  Purchase #5 $8.61   13.760%   $9.7947   $9.79   $9.80   $9.80  
  Purchase #6 $214.69   12.655%   $241.859   $241.86   $241.85   $241.90  
  Purchase #7 $159.55   10.116%   $175.6901   $175.69   $175.70   $175.70  
  7 purchase totals = $927.93       $1,036.9061   $1,036.91   $1,036.95   $1,037.00