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 $53.78   7.847%   $58.0001   $58.00   $58.00   $58.00  
  Purchase #2 $239.38   10.197%   $263.7896   $263.79   $263.80   $263.80  
  Purchase #3 $223.99   8.233%   $242.4311   $242.43   $242.45   $242.40  
  Purchase #4 $168.77   6.361%   $179.5055   $179.51   $179.50   $179.50  
  Purchase #5 $176.30   7.317%   $189.1999   $189.20   $189.20   $189.20  
  Purchase #6 $168.89   3.150%   $174.21   $174.21   $174.20   $174.20  
  Purchase #7 $247.95   7.406%   $266.3132   $266.31   $266.30   $266.30  
  7 purchase totals = $1,279.06       $1,373.4494   $1,373.45   $1,373.45   $1,373.40