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 $200.36   11.786%   $223.9744   $223.97   $223.95   $224.00  
  Purchase #2 $21.93   9.449%   $24.0022   $24.00   $24.00   $24.00  
  Purchase #3 $84.59   12.745%   $95.371   $95.37   $95.35   $95.40  
  Purchase #4 $115.32   6.104%   $122.3591   $122.36   $122.35   $122.40  
  Purchase #5 $87.50   4.215%   $91.1881   $91.19   $91.20   $91.20  
  Purchase #6 $218.93   9.340%   $239.3781   $239.38   $239.40   $239.40  
  Purchase #7 $242.87   13.402%   $275.4194   $275.42   $275.40   $275.40  
  7 purchase totals = $971.50       $1,071.6923   $1,071.69   $1,071.65   $1,071.80