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 $5.30   3.296%   $5.4747   $5.47   $5.45   $5.50  
  Purchase #2 $86.50   4.153%   $90.0923   $90.09   $90.10   $90.10  
  Purchase #3 $38.97   4.265%   $40.6321   $40.63   $40.65   $40.60  
  Purchase #4 $29.93   5.793%   $31.6638   $31.66   $31.65   $31.70  
  Purchase #5 $223.33   12.489%   $251.2217   $251.22   $251.20   $251.20  
  Purchase #6 $197.90   4.414%   $206.6353   $206.64   $206.65   $206.60  
  Purchase #7 $103.76   4.217%   $108.1356   $108.14   $108.15   $108.10  
  7 purchase totals = $685.69       $733.8555   $733.85   $733.85   $733.80