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 $227.74   8.132%   $246.2598   $246.26   $246.25   $246.30  
  Purchase #2 $141.97   4.491%   $148.3459   $148.35   $148.35   $148.30  
  Purchase #3 $214.35   5.643%   $226.4458   $226.45   $226.45   $226.40  
  Purchase #4 $168.41   5.363%   $177.4418   $177.44   $177.45   $177.40  
  Purchase #5 $172.52   5.150%   $181.4048   $181.40   $181.40   $181.40  
  Purchase #6 $111.36   4.698%   $116.5917   $116.59   $116.60   $116.60  
  Purchase #7 $101.91   8.395%   $110.4653   $110.47   $110.45   $110.50  
  7 purchase totals = $1,138.26       $1,206.9551   $1,206.96   $1,206.95   $1,206.90