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 $83.56   5.325%   $88.0096   $88.01   $88.00   $88.00  
  Purchase #2 $198.67   7.183%   $212.9405   $212.94   $212.95   $212.90  
  Purchase #3 $27.99   5.568%   $29.5485   $29.55   $29.55   $29.50  
  Purchase #4 $150.37   13.724%   $171.0068   $171.01   $171.00   $171.00  
  Purchase #5 $67.38   8.815%   $73.3195   $73.32   $73.30   $73.30  
  Purchase #6 $6.72   13.609%   $7.6345   $7.63   $7.65   $7.60  
  Purchase #7 $223.43   7.168%   $239.4455   $239.45   $239.45   $239.40  
  7 purchase totals = $758.12       $821.9049   $821.91   $821.90   $821.70