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 $243.94   5.849%   $258.2081   $258.21   $258.20   $258.20  
  Purchase #2 $215.80   11.545%   $240.7141   $240.71   $240.70   $240.70  
  Purchase #3 $19.58   5.398%   $20.6369   $20.64   $20.65   $20.60  
  Purchase #4 $235.87   13.380%   $267.4294   $267.43   $267.45   $267.40  
  Purchase #5 $15.29   7.662%   $16.4615   $16.46   $16.45   $16.50  
  Purchase #6 $121.86   11.217%   $135.529   $135.53   $135.55   $135.50  
  Purchase #7 $108.54   8.505%   $117.7713   $117.77   $117.75   $117.80  
  7 purchase totals = $960.88       $1,056.7503   $1,056.75   $1,056.75   $1,056.70