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 $203.88   11.340%   $227   $227.00   $227.00   $227.00  
  Purchase #2 $171.77   12.454%   $193.1622   $193.16   $193.15   $193.20  
  Purchase #3 $145.33   8.437%   $157.5915   $157.59   $157.60   $157.60  
  Purchase #4 $200.49   13.755%   $228.0674   $228.07   $228.05   $228.10  
  Purchase #5 $17.68   3.119%   $18.2314   $18.23   $18.25   $18.20  
  Purchase #6 $221.51   6.373%   $235.6268   $235.63   $235.65   $235.60  
  Purchase #7 $171.47   10.356%   $189.2274   $189.23   $189.25   $189.20  
  7 purchase totals = $1,132.13       $1,248.9067   $1,248.91   $1,248.95   $1,248.90