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 $59.98   5.697%   $63.3971   $63.40   $63.40   $63.40  
  Purchase #2 $101.99   11.427%   $113.6444   $113.64   $113.65   $113.60  
  Purchase #3 $142.68   5.583%   $150.6458   $150.65   $150.65   $150.60  
  Purchase #4 $248.43   11.352%   $276.6318   $276.63   $276.65   $276.60  
  Purchase #5 $10.66   10.225%   $11.75   $11.75   $11.75   $11.80  
  Purchase #6 $226.60   6.403%   $241.1092   $241.11   $241.10   $241.10  
  Purchase #7 $215.91   11.589%   $240.9318   $240.93   $240.95   $240.90  
  7 purchase totals = $1,006.25       $1,098.1101   $1,098.11   $1,098.15   $1,098.00