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 $232.41   13.651%   $264.1363   $264.14   $264.15   $264.10  
  Purchase #2 $212.77   10.602%   $235.3279   $235.33   $235.35   $235.30  
  Purchase #3 $14.68   11.281%   $16.3361   $16.34   $16.35   $16.30  
  Purchase #4 $122.41   12.138%   $137.2681   $137.27   $137.25   $137.30  
  Purchase #5 $246.77   9.439%   $270.0626   $270.06   $270.05   $270.10  
  Purchase #6 $176.42   5.397%   $185.9414   $185.94   $185.95   $185.90  
  Purchase #7 $245.96   11.137%   $273.3526   $273.35   $273.35   $273.40  
  7 purchase totals = $1,251.42       $1,382.4250   $1,382.43   $1,382.45   $1,382.40