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 $42.86   10.261%   $47.2579   $47.26   $47.25   $47.30  
  Purchase #2 $192.54   12.525%   $216.6556   $216.66   $216.65   $216.70  
  Purchase #3 $185.74   5.715%   $196.355   $196.36   $196.35   $196.40  
  Purchase #4 $242.82   13.332%   $275.1928   $275.19   $275.20   $275.20  
  Purchase #5 $17.66   8.394%   $19.1424   $19.14   $19.15   $19.10  
  Purchase #6 $171.77   12.654%   $193.5058   $193.51   $193.50   $193.50  
  Purchase #7 $80.72   8.223%   $87.3576   $87.36   $87.35   $87.40  
  7 purchase totals = $934.11       $1,035.4671   $1,035.48   $1,035.45   $1,035.60