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 $219.80   12.528%   $247.3365   $247.34   $247.35   $247.30  
  Purchase #2 $188.55   5.704%   $199.3049   $199.30   $199.30   $199.30  
  Purchase #3 $179.27   4.410%   $187.1758   $187.18   $187.20   $187.20  
  Purchase #4 $130.48   13.582%   $148.2018   $148.20   $148.20   $148.20  
  Purchase #5 $141.25   9.317%   $154.4103   $154.41   $154.40   $154.40  
  Purchase #6 $32.78   4.337%   $34.2017   $34.20   $34.20   $34.20  
  Purchase #7 $245.82   8.800%   $267.4522   $267.45   $267.45   $267.50  
  7 purchase totals = $1,137.95       $1,238.0832   $1,238.08   $1,238.10   $1,238.10