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 $48.61   11.211%   $54.0597   $54.06   $54.05   $54.10  
  Purchase #2 $205.77   4.572%   $215.1778   $215.18   $215.20   $215.20  
  Purchase #3 $221.44   7.402%   $237.831   $237.83   $237.85   $237.80  
  Purchase #4 $242.27   9.397%   $265.0361   $265.04   $265.05   $265.00  
  Purchase #5 $62.34   5.625%   $65.8466   $65.85   $65.85   $65.80  
  Purchase #6 $32.37   11.828%   $36.1987   $36.20   $36.20   $36.20  
  Purchase #7 $120.61   4.651%   $126.2196   $126.22   $126.20   $126.20  
  7 purchase totals = $933.41       $1,000.3695   $1,000.38   $1,000.40   $1,000.30