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 $48.46   4.470%   $50.6262   $50.63   $50.65   $50.60  
  Purchase #2 $222.50   11.246%   $247.5224   $247.52   $247.50   $247.50  
  Purchase #3 $221.88   5.721%   $234.5738   $234.57   $234.55   $234.60  
  Purchase #4 $234.73   5.296%   $247.1613   $247.16   $247.15   $247.20  
  Purchase #5 $62.77   7.163%   $67.2662   $67.27   $67.25   $67.30  
  Purchase #6 $17.72   9.501%   $19.4036   $19.40   $19.40   $19.40  
  Purchase #7 $243.74   8.719%   $264.9917   $264.99   $265.00   $265.00  
  7 purchase totals = $1,051.80       $1,131.5452   $1,131.54   $1,131.50   $1,131.60