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 $59.68   5.401%   $62.9033   $62.90   $62.90   $62.90  
  Purchase #2 $99.93   13.110%   $113.0308   $113.03   $113.05   $113.00  
  Purchase #3 $23.58   4.379%   $24.6126   $24.61   $24.60   $24.60  
  Purchase #4 $32.75   10.358%   $36.1422   $36.14   $36.15   $36.10  
  Purchase #5 $22.57   6.789%   $24.1023   $24.10   $24.10   $24.10  
  Purchase #6 $84.44   5.306%   $88.9204   $88.92   $88.90   $88.90  
  Purchase #7 $227.29   4.855%   $238.3249   $238.32   $238.30   $238.30  
  7 purchase totals = $550.24       $588.0365   $588.02   $588.00   $587.90