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 $203.80   11.191%   $226.6073   $226.61   $226.60   $226.60  
  Purchase #2 $196.98   10.141%   $216.9557   $216.96   $216.95   $217.00  
  Purchase #3 $46.71   12.734%   $52.6581   $52.66   $52.65   $52.70  
  Purchase #4 $97.50   3.666%   $101.0744   $101.07   $101.05   $101.10  
  Purchase #5 $170.82   9.448%   $186.9591   $186.96   $186.95   $187.00  
  Purchase #6 $65.61   8.226%   $71.0071   $71.01   $71.00   $71.00  
  Purchase #7 $213.92   8.319%   $231.716   $231.72   $231.70   $231.70  
  7 purchase totals = $995.34       $1,086.9777   $1,086.99   $1,086.90   $1,087.10