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 $90.57   8.790%   $98.5311   $98.53   $98.55   $98.50  
  Purchase #2 $220.59   6.102%   $234.0504   $234.05   $234.05   $234.10  
  Purchase #3 $197.27   11.288%   $219.5378   $219.54   $219.55   $219.50  
  Purchase #4 $15.32   9.805%   $16.8221   $16.82   $16.80   $16.80  
  Purchase #5 $200.69   6.373%   $213.48   $213.48   $213.50   $213.50  
  Purchase #6 $60.25   6.145%   $63.9524   $63.95   $63.95   $64.00  
  Purchase #7 $103.93   3.787%   $107.8658   $107.87   $107.85   $107.90  
  7 purchase totals = $888.62       $954.2396   $954.24   $954.25   $954.30