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 $163.80   11.692%   $182.9515   $182.95   $182.95   $183.00  
  Purchase #2 $30.45   12.572%   $34.2782   $34.28   $34.30   $34.30  
  Purchase #3 $142.85   7.777%   $153.9594   $153.96   $153.95   $154.00  
  Purchase #4 $153.57   8.682%   $166.9029   $166.90   $166.90   $166.90  
  Purchase #5 $158.33   6.644%   $168.8494   $168.85   $168.85   $168.80  
  Purchase #6 $37.51   6.709%   $40.0265   $40.03   $40.05   $40.00  
  Purchase #7 $174.26   6.133%   $184.9474   $184.95   $184.95   $184.90  
  7 purchase totals = $860.77       $931.9153   $931.92   $931.95   $931.90