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 $230.63   9.807%   $253.2479   $253.25   $253.25   $253.20  
  Purchase #2 $58.63   6.838%   $62.6391   $62.64   $62.65   $62.60  
  Purchase #3 $155.90   6.701%   $166.3469   $166.35   $166.35   $166.30  
  Purchase #4 $200.44   12.379%   $225.2525   $225.25   $225.25   $225.30  
  Purchase #5 $96.58   7.779%   $104.093   $104.09   $104.10   $104.10  
  Purchase #6 $247.58   11.311%   $275.5838   $275.58   $275.60   $275.60  
  Purchase #7 $113.27   12.789%   $127.7561   $127.76   $127.75   $127.80  
  7 purchase totals = $1,103.03       $1,214.9193   $1,214.92   $1,214.95   $1,214.90