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 $57.61   8.722%   $62.6347   $62.63   $62.65   $62.60  
  Purchase #2 $242.78   11.446%   $270.5686   $270.57   $270.55   $270.60  
  Purchase #3 $100.52   13.840%   $114.432   $114.43   $114.45   $114.40  
  Purchase #4 $15.59   5.283%   $16.4136   $16.41   $16.40   $16.40  
  Purchase #5 $60.75   10.363%   $67.0455   $67.05   $67.05   $67.00  
  Purchase #6 $215.46   6.540%   $229.5511   $229.55   $229.55   $229.60  
  Purchase #7 $134.45   3.519%   $139.1813   $139.18   $139.20   $139.20  
  7 purchase totals = $827.16       $899.8268   $899.82   $899.85   $899.80