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 $48.49   8.472%   $52.5981   $52.60   $52.60   $52.60  
  Purchase #2 $145.60   11.488%   $162.3265   $162.33   $162.35   $162.30  
  Purchase #3 $159.63   10.453%   $176.3161   $176.32   $176.30   $176.30  
  Purchase #4 $21.56   5.767%   $22.8034   $22.80   $22.80   $22.80  
  Purchase #5 $235.58   11.571%   $262.839   $262.84   $262.85   $262.80  
  Purchase #6 $235.34   13.190%   $266.3813   $266.38   $266.40   $266.40  
  Purchase #7 $123.33   3.781%   $127.9931   $127.99   $128.00   $128.00  
  7 purchase totals = $969.53       $1,071.2575   $1,071.26   $1,071.30   $1,071.20