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 $206.95   3.205%   $213.5827   $213.58   $213.60   $213.60  
  Purchase #2 $97.94   13.405%   $111.0689   $111.07   $111.05   $111.10  
  Purchase #3 $205.52   9.809%   $225.6795   $225.68   $225.70   $225.70  
  Purchase #4 $245.63   6.739%   $262.183   $262.18   $262.20   $262.20  
  Purchase #5 $225.81   13.722%   $256.7956   $256.80   $256.80   $256.80  
  Purchase #6 $169.35   10.675%   $187.4281   $187.43   $187.45   $187.40  
  Purchase #7 $17.88   5.469%   $18.8579   $18.86   $18.85   $18.90  
  7 purchase totals = $1,169.08       $1,275.5957   $1,275.60   $1,275.65   $1,275.70