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 $65.90   5.842%   $69.7499   $69.75   $69.75   $69.70  
  Purchase #2 $249.35   9.463%   $272.946   $272.95   $272.95   $272.90  
  Purchase #3 $234.40   9.543%   $256.7688   $256.77   $256.75   $256.80  
  Purchase #4 $57.44   11.845%   $64.2438   $64.24   $64.25   $64.20  
  Purchase #5 $175.33   3.558%   $181.5682   $181.57   $181.55   $181.60  
  Purchase #6 $109.29   13.547%   $124.0955   $124.10   $124.10   $124.10  
  Purchase #7 $34.59   12.320%   $38.8515   $38.85   $38.85   $38.90  
  7 purchase totals = $926.30       $1,008.2237   $1,008.23   $1,008.20   $1,008.20