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 $206.57   9.303%   $225.7872   $225.79   $225.80   $225.80  
  Purchase #2 $165.42   8.165%   $178.9265   $178.93   $178.95   $178.90  
  Purchase #3 $235.66   3.409%   $243.6936   $243.69   $243.70   $243.70  
  Purchase #4 $205.61   5.568%   $217.0584   $217.06   $217.05   $217.10  
  Purchase #5 $24.51   10.137%   $26.9946   $26.99   $27.00   $27.00  
  Purchase #6 $78.43   11.282%   $87.2785   $87.28   $87.30   $87.30  
  Purchase #7 $68.75   6.852%   $73.4608   $73.46   $73.45   $73.50  
  7 purchase totals = $984.95       $1,053.1996   $1,053.20   $1,053.25   $1,053.30