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 $94.62   7.720%   $101.9247   $101.92   $101.90   $101.90  
  Purchase #2 $187.37   12.598%   $210.9749   $210.97   $210.95   $211.00  
  Purchase #3 $221.40   7.654%   $238.346   $238.35   $238.35   $238.30  
  Purchase #4 $235.95   10.712%   $261.225   $261.23   $261.25   $261.20  
  Purchase #5 $68.26   9.259%   $74.5802   $74.58   $74.60   $74.60  
  Purchase #6 $143.42   12.597%   $161.4866   $161.49   $161.50   $161.50  
  Purchase #7 $39.30   10.235%   $43.3224   $43.32   $43.30   $43.30  
  7 purchase totals = $990.32       $1,091.8598   $1,091.86   $1,091.85   $1,091.80