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 $67.62   5.376%   $71.2553   $71.26   $71.25   $71.30  
  Purchase #2 $216.72   8.605%   $235.3688   $235.37   $235.35   $235.40  
  Purchase #3 $244.39   7.702%   $263.2129   $263.21   $263.20   $263.20  
  Purchase #4 $63.37   7.430%   $68.0784   $68.08   $68.10   $68.10  
  Purchase #5 $32.39   13.125%   $36.6412   $36.64   $36.65   $36.60  
  Purchase #6 $240.58   3.115%   $248.0741   $248.07   $248.05   $248.10  
  Purchase #7 $30.44   4.722%   $31.8774   $31.88   $31.90   $31.90  
  7 purchase totals = $895.51       $954.5081   $954.51   $954.50   $954.60