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 $193.36   13.657%   $219.7672   $219.77   $219.75   $219.80  
  Purchase #2 $177.68   4.166%   $185.0821   $185.08   $185.10   $185.10  
  Purchase #3 $55.80   12.358%   $62.6958   $62.70   $62.70   $62.70  
  Purchase #4 $92.51   4.337%   $96.5222   $96.52   $96.50   $96.50  
  Purchase #5 $204.61   5.724%   $216.3219   $216.32   $216.30   $216.30  
  Purchase #6 $5.89   10.387%   $6.5018   $6.50   $6.50   $6.50  
  Purchase #7 $216.46   8.460%   $234.7725   $234.77   $234.75   $234.80  
  7 purchase totals = $946.31       $1,021.6635   $1,021.66   $1,021.60   $1,021.70