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 $245.55   11.179%   $273   $273.00   $273.00   $273.00  
  Purchase #2 $243.83   8.381%   $264.2654   $264.27   $264.25   $264.30  
  Purchase #3 $118.30   7.425%   $127.0838   $127.08   $127.10   $127.10  
  Purchase #4 $30.43   12.529%   $34.2426   $34.24   $34.25   $34.20  
  Purchase #5 $86.66   7.220%   $92.9169   $92.92   $92.90   $92.90  
  Purchase #6 $159.28   5.274%   $167.6804   $167.68   $167.70   $167.70  
  Purchase #7 $201.62   12.802%   $227.4314   $227.43   $227.45   $227.40  
  7 purchase totals = $1,085.67       $1,186.6205   $1,186.62   $1,186.65   $1,186.60