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 $54.49   12.311%   $61.1983   $61.20   $61.20   $61.20  
  Purchase #2 $179.30   9.308%   $195.9892   $195.99   $196.00   $196.00  
  Purchase #3 $120.44   3.483%   $124.6349   $124.63   $124.65   $124.60  
  Purchase #4 $57.44   12.226%   $64.4626   $64.46   $64.45   $64.50  
  Purchase #5 $185.50   13.522%   $210.5833   $210.58   $210.60   $210.60  
  Purchase #6 $201.49   5.615%   $212.8037   $212.80   $212.80   $212.80  
  Purchase #7 $129.86   11.715%   $145.0731   $145.07   $145.05   $145.10  
  7 purchase totals = $928.52       $1,014.7451   $1,014.73   $1,014.75   $1,014.80