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 $192.95   11.324%   $214.7997   $214.80   $214.80   $214.80  
  Purchase #2 $112.25   9.305%   $122.6949   $122.69   $122.70   $122.70  
  Purchase #3 $29.89   6.790%   $31.9195   $31.92   $31.90   $31.90  
  Purchase #4 $245.92   8.534%   $266.9068   $266.91   $266.90   $266.90  
  Purchase #5 $44.35   7.424%   $47.6425   $47.64   $47.65   $47.60  
  Purchase #6 $185.32   10.337%   $204.4765   $204.48   $204.50   $204.50  
  Purchase #7 $155.47   3.104%   $160.2958   $160.30   $160.30   $160.30  
  7 purchase totals = $966.15       $1,048.7357   $1,048.74   $1,048.75   $1,048.70