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 $188.39   10.227%   $207.6566   $207.66   $207.65   $207.70  
  Purchase #2 $219.26   7.825%   $236.4171   $236.42   $236.40   $236.40  
  Purchase #3 $14.99   12.589%   $16.8771   $16.88   $16.90   $16.90  
  Purchase #4 $224.78   10.324%   $247.9863   $247.99   $248.00   $248.00  
  Purchase #5 $221.33   13.532%   $251.2804   $251.28   $251.30   $251.30  
  Purchase #6 $27.69   11.835%   $30.9671   $30.97   $30.95   $31.00  
  Purchase #7 $52.67   4.446%   $55.0117   $55.01   $55.00   $55.00  
  7 purchase totals = $949.11       $1,046.1963   $1,046.21   $1,046.20   $1,046.30