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 $113.88   13.862%   $129.666   $129.67   $129.65   $129.70  
  Purchase #2 $22.69   8.541%   $24.628   $24.63   $24.65   $24.60  
  Purchase #3 $169.74   3.515%   $175.7064   $175.71   $175.70   $175.70  
  Purchase #4 $117.74   5.371%   $124.0638   $124.06   $124.05   $124.10  
  Purchase #5 $250.65   12.256%   $281.3697   $281.37   $281.35   $281.40  
  Purchase #6 $138.74   12.513%   $156.1005   $156.10   $156.10   $156.10  
  Purchase #7 $247.51   11.294%   $275.4638   $275.46   $275.45   $275.50  
  7 purchase totals = $1,060.95       $1,166.9982   $1,167.00   $1,166.95   $1,167.10