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 $185.90   8.266%   $201.2665   $201.27   $201.25   $201.30  
  Purchase #2 $223.93   8.603%   $243.1947   $243.19   $243.20   $243.20  
  Purchase #3 $108.99   12.407%   $122.5124   $122.51   $122.50   $122.50  
  Purchase #4 $235.61   12.825%   $265.827   $265.83   $265.85   $265.80  
  Purchase #5 $60.31   13.553%   $68.4838   $68.48   $68.50   $68.50  
  Purchase #6 $60.62   3.523%   $62.7556   $62.76   $62.75   $62.80  
  Purchase #7 $194.41   11.766%   $217.2843   $217.28   $217.30   $217.30  
  7 purchase totals = $1,069.77       $1,181.3243   $1,181.32   $1,181.35   $1,181.40