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 $58.49   8.244%   $63.3119   $63.31   $63.30   $63.30  
  Purchase #2 $205.80   13.689%   $233.972   $233.97   $233.95   $234.00  
  Purchase #3 $34.79   6.482%   $37.0451   $37.05   $37.05   $37.00  
  Purchase #4 $186.96   3.527%   $193.5541   $193.55   $193.55   $193.60  
  Purchase #5 $36.30   10.241%   $40.0175   $40.02   $40.00   $40.00  
  Purchase #6 $115.45   5.614%   $121.9314   $121.93   $121.95   $121.90  
  Purchase #7 $171.48   4.509%   $179.212   $179.21   $179.20   $179.20  
  7 purchase totals = $809.27       $869.0440   $869.04   $869.00   $869.00