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 $134.49   10.235%   $148.2551   $148.26   $148.25   $148.30  
  Purchase #2 $53.57   13.602%   $60.8566   $60.86   $60.85   $60.90  
  Purchase #3 $65.80   6.369%   $69.9908   $69.99   $70.00   $70.00  
  Purchase #4 $229.86   8.126%   $248.5384   $248.54   $248.55   $248.50  
  Purchase #5 $235.74   6.764%   $251.6855   $251.69   $251.70   $251.70  
  Purchase #6 $99.80   8.211%   $107.9946   $107.99   $108.00   $108.00  
  Purchase #7 $137.46   4.438%   $143.5605   $143.56   $143.55   $143.60  
  7 purchase totals = $956.72       $1,030.8815   $1,030.89   $1,030.90   $1,031.00