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 $64.96   6.266%   $69.0304   $69.03   $69.05   $69.00  
  Purchase #2 $165.26   10.313%   $182.3033   $182.30   $182.30   $182.30  
  Purchase #3 $97.26   8.227%   $105.2616   $105.26   $105.25   $105.30  
  Purchase #4 $49.34   9.641%   $54.0969   $54.10   $54.10   $54.10  
  Purchase #5 $76.57   4.646%   $80.1274   $80.13   $80.15   $80.10  
  Purchase #6 $168.58   13.440%   $191.2372   $191.24   $191.25   $191.20  
  Purchase #7 $21.72   8.486%   $23.5632   $23.56   $23.55   $23.60  
  7 purchase totals = $643.69       $705.6200   $705.62   $705.65   $705.60