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 $231.86   6.508%   $246.9494   $246.95   $246.95   $246.90  
  Purchase #2 $167.82   3.337%   $173.4202   $173.42   $173.40   $173.40  
  Purchase #3 $47.57   12.391%   $53.4644   $53.46   $53.45   $53.50  
  Purchase #4 $126.65   11.448%   $141.1489   $141.15   $141.15   $141.10  
  Purchase #5 $212.43   6.661%   $226.58   $226.58   $226.60   $226.60  
  Purchase #6 $192.27   10.299%   $212.0719   $212.07   $212.05   $212.10  
  Purchase #7 $239.62   11.796%   $267.8856   $267.89   $267.90   $267.90  
  7 purchase totals = $1,218.22       $1,321.5204   $1,321.52   $1,321.50   $1,321.50