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 $130.82   13.483%   $148.4585   $148.46   $148.45   $148.50  
  Purchase #2 $245.84   6.310%   $261.3525   $261.35   $261.35   $261.40  
  Purchase #3 $118.26   8.171%   $127.923   $127.92   $127.90   $127.90  
  Purchase #4 $126.91   5.738%   $134.1921   $134.19   $134.20   $134.20  
  Purchase #5 $14.45   9.610%   $15.8386   $15.84   $15.85   $15.80  
  Purchase #6 $73.64   8.628%   $79.9937   $79.99   $80.00   $80.00  
  Purchase #7 $231.44   8.364%   $250.7976   $250.80   $250.80   $250.80  
  7 purchase totals = $941.36       $1,018.5560   $1,018.55   $1,018.55   $1,018.60