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 $84.56   11.754%   $94.4992   $94.50   $94.50   $94.50  
  Purchase #2 $114.32   8.678%   $124.2407   $124.24   $124.25   $124.20  
  Purchase #3 $199.70   7.654%   $214.985   $214.99   $215.00   $215.00  
  Purchase #4 $124.43   9.545%   $136.3068   $136.31   $136.30   $136.30  
  Purchase #5 $181.54   10.693%   $200.9521   $200.95   $200.95   $201.00  
  Purchase #6 $134.33   12.449%   $151.0527   $151.05   $151.05   $151.10  
  Purchase #7 $154.93   7.437%   $166.4521   $166.45   $166.45   $166.50  
  7 purchase totals = $993.81       $1,088.4886   $1,088.49   $1,088.50   $1,088.60