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 $56.33   4.583%   $58.9116   $58.91   $58.90   $58.90  
  Purchase #2 $214.74   8.191%   $232.3294   $232.33   $232.35   $232.30  
  Purchase #3 $20.83   10.606%   $23.0392   $23.04   $23.05   $23.00  
  Purchase #4 $195.53   8.475%   $212.1012   $212.10   $212.10   $212.10  
  Purchase #5 $105.70   13.208%   $119.6609   $119.66   $119.65   $119.70  
  Purchase #6 $158.65   13.470%   $180.0202   $180.02   $180.00   $180.00  
  Purchase #7 $223.61   12.371%   $251.2728   $251.27   $251.25   $251.30  
  7 purchase totals = $975.39       $1,077.3353   $1,077.33   $1,077.30   $1,077.30