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 $68.74   9.639%   $75.3658   $75.37   $75.35   $75.40  
  Purchase #2 $127.75   10.797%   $141.5432   $141.54   $141.55   $141.50  
  Purchase #3 $78.79   9.404%   $86.1994   $86.20   $86.20   $86.20  
  Purchase #4 $216.72   12.175%   $243.1057   $243.11   $243.10   $243.10  
  Purchase #5 $222.45   5.296%   $234.231   $234.23   $234.25   $234.20  
  Purchase #6 $196.76   7.734%   $211.9774   $211.98   $212.00   $212.00  
  Purchase #7 $13.27   7.240%   $14.2307   $14.23   $14.25   $14.20  
  7 purchase totals = $924.48       $1,006.6532   $1,006.66   $1,006.70   $1,006.60