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 $73.65   13.857%   $83.8557   $83.86   $83.85   $83.90  
  Purchase #2 $198.99   10.257%   $219.4004   $219.40   $219.40   $219.40  
  Purchase #3 $68.40   12.352%   $76.8488   $76.85   $76.85   $76.80  
  Purchase #4 $114.60   11.493%   $127.771   $127.77   $127.75   $127.80  
  Purchase #5 $184.79   9.160%   $201.7168   $201.72   $201.70   $201.70  
  Purchase #6 $18.32   11.403%   $20.409   $20.41   $20.40   $20.40  
  Purchase #7 $6.39   9.265%   $6.982   $6.98   $7.00   $7.00  
  7 purchase totals = $665.14       $736.9837   $736.99   $736.95   $737.00