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 $95.94   8.207%   $103.8138   $103.81   $103.80   $103.80  
  Purchase #2 $195.57   12.598%   $220.2079   $220.21   $220.20   $220.20  
  Purchase #3 $113.35   3.553%   $117.3773   $117.38   $117.40   $117.40  
  Purchase #4 $53.34   13.468%   $60.5238   $60.52   $60.50   $60.50  
  Purchase #5 $128.96   13.191%   $145.9711   $145.97   $145.95   $146.00  
  Purchase #6 $221.62   11.334%   $246.7384   $246.74   $246.75   $246.70  
  Purchase #7 $185.59   10.490%   $205.0584   $205.06   $205.05   $205.10  
  7 purchase totals = $994.37       $1,099.6907   $1,099.69   $1,099.65   $1,099.70