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 $222.58   9.242%   $243.1508   $243.15   $243.15   $243.20  
  Purchase #2 $120.91   10.341%   $133.4133   $133.41   $133.40   $133.40  
  Purchase #3 $8.26   7.104%   $8.8468   $8.85   $8.85   $8.80  
  Purchase #4 $148.65   3.791%   $154.2853   $154.29   $154.30   $154.30  
  Purchase #5 $206.56   13.257%   $233.9437   $233.94   $233.95   $233.90  
  Purchase #6 $164.34   7.107%   $176.0196   $176.02   $176.00   $176.00  
  Purchase #7 $57.99   12.369%   $65.1628   $65.16   $65.15   $65.20  
  7 purchase totals = $929.29       $1,014.8223   $1,014.82   $1,014.80   $1,014.80