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 $171.87   8.731%   $186.876   $186.88   $186.90   $186.90  
  Purchase #2 $161.58   6.480%   $172.0504   $172.05   $172.05   $172.10  
  Purchase #3 $114.52   11.424%   $127.6028   $127.60   $127.60   $127.60  
  Purchase #4 $238.83   9.698%   $261.9917   $261.99   $262.00   $262.00  
  Purchase #5 $62.80   13.351%   $71.1844   $71.18   $71.20   $71.20  
  Purchase #6 $65.79   5.674%   $69.5229   $69.52   $69.50   $69.50  
  Purchase #7 $166.25   10.769%   $184.1535   $184.15   $184.15   $184.20  
  7 purchase totals = $981.64       $1,073.3817   $1,073.37   $1,073.40   $1,073.50