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 $220.89   9.108%   $241.0087   $241.01   $241.00   $241.00  
  Purchase #2 $245.29   11.693%   $273.9718   $273.97   $273.95   $274.00  
  Purchase #3 $218.66   6.541%   $232.9626   $232.96   $232.95   $233.00  
  Purchase #4 $25.66   9.434%   $28.0808   $28.08   $28.10   $28.10  
  Purchase #5 $135.48   5.523%   $142.9626   $142.96   $142.95   $143.00  
  Purchase #6 $223.72   8.110%   $241.8637   $241.86   $241.85   $241.90  
  Purchase #7 $215.47   3.771%   $223.5954   $223.60   $223.60   $223.60  
  7 purchase totals = $1,285.17       $1,384.4456   $1,384.44   $1,384.40   $1,384.60