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 $169.46   12.628%   $190.8594   $190.86   $190.85   $190.90  
  Purchase #2 $241.29   13.549%   $273.9824   $273.98   $274.00   $274.00  
  Purchase #3 $113.48   12.605%   $127.7842   $127.78   $127.80   $127.80  
  Purchase #4 $60.68   4.716%   $63.5417   $63.54   $63.55   $63.50  
  Purchase #5 $208.58   5.609%   $220.2793   $220.28   $220.30   $220.30  
  Purchase #6 $73.89   7.340%   $79.3135   $79.31   $79.30   $79.30  
  Purchase #7 $73.54   11.436%   $81.95   $81.95   $81.95   $82.00  
  7 purchase totals = $940.92       $1,037.7105   $1,037.70   $1,037.75   $1,037.80