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 $214.26   9.869%   $235.4053   $235.41   $235.40   $235.40  
  Purchase #2 $157.99   4.532%   $165.1501   $165.15   $165.15   $165.20  
  Purchase #3 $158.62   9.103%   $173.0592   $173.06   $173.05   $173.10  
  Purchase #4 $54.29   9.170%   $59.2684   $59.27   $59.25   $59.30  
  Purchase #5 $157.73   3.595%   $163.4004   $163.40   $163.40   $163.40  
  Purchase #6 $56.32   3.481%   $58.2805   $58.28   $58.30   $58.30  
  Purchase #7 $217.99   3.193%   $224.9504   $224.95   $224.95   $225.00  
  7 purchase totals = $1,017.20       $1,079.5143   $1,079.52   $1,079.50   $1,079.70