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 $94.82   3.827%   $98.4488   $98.45   $98.45   $98.40  
  Purchase #2 $175.49   9.406%   $191.9966   $192.00   $192.00   $192.00  
  Purchase #3 $104.26   10.372%   $115.0738   $115.07   $115.05   $115.10  
  Purchase #4 $9.97   13.235%   $11.2895   $11.29   $11.30   $11.30  
  Purchase #5 $132.99   7.209%   $142.5772   $142.58   $142.60   $142.60  
  Purchase #6 $189.47   7.486%   $203.6537   $203.65   $203.65   $203.70  
  Purchase #7 $238.54   10.309%   $263.1311   $263.13   $263.15   $263.10  
  7 purchase totals = $945.54       $1,026.1707   $1,026.17   $1,026.20   $1,026.20