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 $55.66   11.393%   $62.0013   $62.00   $62.00   $62.00  
  Purchase #2 $223.41   4.827%   $234.194   $234.19   $234.20   $234.20  
  Purchase #3 $116.91   7.783%   $126.0091   $126.01   $126.00   $126.00  
  Purchase #4 $124.47   4.653%   $130.2616   $130.26   $130.25   $130.30  
  Purchase #5 $145.72   4.159%   $151.7805   $151.78   $151.80   $151.80  
  Purchase #6 $234.90   8.275%   $254.338   $254.34   $254.35   $254.30  
  Purchase #7 $72.40   11.870%   $80.9939   $80.99   $81.00   $81.00  
  7 purchase totals = $973.47       $1,039.5784   $1,039.57   $1,039.60   $1,039.60