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 $246.62   12.111%   $276.4881   $276.49   $276.50   $276.50  
  Purchase #2 $68.59   5.384%   $72.2829   $72.28   $72.30   $72.30  
  Purchase #3 $205.93   5.663%   $217.5918   $217.59   $217.60   $217.60  
  Purchase #4 $189.42   6.158%   $201.0845   $201.08   $201.10   $201.10  
  Purchase #5 $221.97   11.834%   $248.2379   $248.24   $248.25   $248.20  
  Purchase #6 $69.80   13.122%   $78.9592   $78.96   $78.95   $79.00  
  Purchase #7 $236.92   7.461%   $254.5966   $254.60   $254.60   $254.60  
  7 purchase totals = $1,239.25       $1,349.2410   $1,349.24   $1,349.30   $1,349.30