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 $146.73   12.394%   $164.9157   $164.92   $164.90   $164.90  
  Purchase #2 $163.91   6.114%   $173.9315   $173.93   $173.95   $173.90  
  Purchase #3 $74.83   13.351%   $84.8206   $84.82   $84.80   $84.80  
  Purchase #4 $244.95   6.379%   $260.5754   $260.58   $260.60   $260.60  
  Purchase #5 $109.36   12.113%   $122.6068   $122.61   $122.60   $122.60  
  Purchase #6 $10.71   13.134%   $12.1167   $12.12   $12.10   $12.10  
  Purchase #7 $26.80   10.347%   $29.573   $29.57   $29.55   $29.60  
  7 purchase totals = $777.29       $848.5397   $848.55   $848.50   $848.50