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 $147.69   13.729%   $167.9664   $167.97   $167.95   $168.00  
  Purchase #2 $198.32   10.384%   $218.9135   $218.91   $218.90   $218.90  
  Purchase #3 $24.74   8.126%   $26.7504   $26.75   $26.75   $26.80  
  Purchase #4 $62.27   11.842%   $69.644   $69.64   $69.65   $69.60  
  Purchase #5 $95.57   3.118%   $98.5499   $98.55   $98.55   $98.50  
  Purchase #6 $94.99   9.140%   $103.6721   $103.67   $103.65   $103.70  
  Purchase #7 $71.47   4.344%   $74.5747   $74.57   $74.55   $74.60  
  7 purchase totals = $695.05       $760.0710   $760.06   $760.00   $760.10