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 $207.68   8.812%   $225.9808   $225.98   $226.00   $226.00  
  Purchase #2 $151.50   4.245%   $157.9312   $157.93   $157.95   $157.90  
  Purchase #3 $154.61   5.146%   $162.5662   $162.57   $162.55   $162.60  
  Purchase #4 $75.52   6.584%   $80.4922   $80.49   $80.50   $80.50  
  Purchase #5 $67.71   6.708%   $72.252   $72.25   $72.25   $72.30  
  Purchase #6 $91.46   12.815%   $103.1806   $103.18   $103.20   $103.20  
  Purchase #7 $159.65   6.631%   $170.2364   $170.24   $170.25   $170.20  
  7 purchase totals = $908.13       $972.6394   $972.64   $972.70   $972.70