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 $58.65   10.133%   $64.593   $64.59   $64.60   $64.60  
  Purchase #2 $54.64   9.636%   $59.9051   $59.91   $59.90   $59.90  
  Purchase #3 $69.52   5.205%   $73.1385   $73.14   $73.15   $73.10  
  Purchase #4 $63.81   7.237%   $68.4279   $68.43   $68.45   $68.40  
  Purchase #5 $193.78   7.352%   $208.0267   $208.03   $208.05   $208.00  
  Purchase #6 $231.82   5.730%   $245.1033   $245.10   $245.10   $245.10  
  Purchase #7 $166.38   11.183%   $184.9863   $184.99   $185.00   $185.00  
  7 purchase totals = $838.60       $904.1808   $904.19   $904.25   $904.10