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 $48.55   6.607%   $51.7577   $51.76   $51.75   $51.80  
  Purchase #2 $191.88   10.293%   $211.6302   $211.63   $211.65   $211.60  
  Purchase #3 $136.98   11.597%   $152.8656   $152.87   $152.85   $152.90  
  Purchase #4 $105.26   8.574%   $114.285   $114.29   $114.30   $114.30  
  Purchase #5 $192.95   9.663%   $211.5948   $211.59   $211.60   $211.60  
  Purchase #6 $136.77   12.332%   $153.6365   $153.64   $153.65   $153.60  
  Purchase #7 $60.99   10.159%   $67.186   $67.19   $67.20   $67.20  
  7 purchase totals = $873.38       $962.9558   $962.97   $963.00   $963.00