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 $62.34   11.627%   $69.5883   $69.59   $69.60   $69.60  
  Purchase #2 $40.97   4.432%   $42.7858   $42.79   $42.80   $42.80  
  Purchase #3 $132.53   11.114%   $147.2594   $147.26   $147.25   $147.30  
  Purchase #4 $225.58   5.449%   $237.8719   $237.87   $237.85   $237.90  
  Purchase #5 $224.58   13.217%   $254.2627   $254.26   $254.25   $254.30  
  Purchase #6 $115.43   10.538%   $127.594   $127.59   $127.60   $127.60  
  Purchase #7 $60.30   5.801%   $63.798   $63.80   $63.80   $63.80  
  7 purchase totals = $861.73       $943.1601   $943.16   $943.15   $943.30