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 $234.30   5.281%   $246.6734   $246.67   $246.65   $246.70  
  Purchase #2 $169.35   13.558%   $192.3105   $192.31   $192.30   $192.30  
  Purchase #3 $11.46   13.392%   $12.9947   $12.99   $13.00   $13.00  
  Purchase #4 $46.31   3.638%   $47.9948   $47.99   $48.00   $48.00  
  Purchase #5 $167.77   8.484%   $182.0036   $182.00   $182.00   $182.00  
  Purchase #6 $57.43   7.245%   $61.5908   $61.59   $61.60   $61.60  
  Purchase #7 $12.70   12.489%   $14.2861   $14.29   $14.30   $14.30  
  7 purchase totals = $699.32       $757.8539   $757.84   $757.85   $757.90