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 $147.39   10.632%   $163.0605   $163.06   $163.05   $163.10  
  Purchase #2 $68.34   7.243%   $73.2899   $73.29   $73.30   $73.30  
  Purchase #3 $11.40   9.851%   $12.523   $12.52   $12.50   $12.50  
  Purchase #4 $203.73   8.444%   $220.933   $220.93   $220.95   $220.90  
  Purchase #5 $197.29   8.115%   $213.3001   $213.30   $213.30   $213.30  
  Purchase #6 $99.85   5.523%   $105.3647   $105.36   $105.35   $105.40  
  Purchase #7 $113.81   7.657%   $122.5244   $122.52   $122.50   $122.50  
  7 purchase totals = $841.81       $910.9956   $910.98   $910.95   $911.00