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 $246.99   4.270%   $257.5365   $257.54   $257.55   $257.50  
  Purchase #2 $188.42   6.458%   $200.5882   $200.59   $200.60   $200.60  
  Purchase #3 $82.58   3.500%   $85.4703   $85.47   $85.45   $85.50  
  Purchase #4 $195.70   3.498%   $202.5456   $202.55   $202.55   $202.50  
  Purchase #5 $147.33   6.609%   $157.067   $157.07   $157.05   $157.10  
  Purchase #6 $194.48   3.297%   $200.892   $200.89   $200.90   $200.90  
  Purchase #7 $145.51   5.292%   $153.2104   $153.21   $153.20   $153.20  
  7 purchase totals = $1,201.01       $1,257.3100   $1,257.32   $1,257.30   $1,257.30