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 $154.96   9.434%   $169.5789   $169.58   $169.60   $169.60  
  Purchase #2 $116.27   8.646%   $126.3227   $126.32   $126.30   $126.30  
  Purchase #3 $209.60   5.382%   $220.8807   $220.88   $220.90   $220.90  
  Purchase #4 $63.80   3.562%   $66.0726   $66.07   $66.05   $66.10  
  Purchase #5 $52.33   9.705%   $57.4086   $57.41   $57.40   $57.40  
  Purchase #6 $146.39   3.732%   $151.8533   $151.85   $151.85   $151.90  
  Purchase #7 $46.84   5.687%   $49.5038   $49.50   $49.50   $49.50  
  7 purchase totals = $790.19       $841.6206   $841.61   $841.60   $841.70