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 $203.76   11.169%   $226.518   $226.52   $226.50   $226.50  
  Purchase #2 $225.65   13.472%   $256.0496   $256.05   $256.05   $256.00  
  Purchase #3 $36.86   4.413%   $38.4866   $38.49   $38.50   $38.50  
  Purchase #4 $157.74   8.449%   $171.0675   $171.07   $171.05   $171.10  
  Purchase #5 $182.34   11.521%   $203.3474   $203.35   $203.35   $203.30  
  Purchase #6 $15.45   10.181%   $17.023   $17.02   $17.00   $17.00  
  Purchase #7 $177.29   5.577%   $187.1775   $187.18   $187.20   $187.20  
  7 purchase totals = $999.09       $1,099.6696   $1,099.68   $1,099.65   $1,099.60