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 $165.37   10.473%   $182.6892   $182.69   $182.70   $182.70  
  Purchase #2 $89.73   13.186%   $101.5618   $101.56   $101.55   $101.60  
  Purchase #3 $181.58   12.849%   $204.9112   $204.91   $204.90   $204.90  
  Purchase #4 $58.89   7.241%   $63.1542   $63.15   $63.15   $63.20  
  Purchase #5 $141.65   3.419%   $146.493   $146.49   $146.50   $146.50  
  Purchase #6 $163.62   3.854%   $169.9259   $169.93   $169.95   $169.90  
  Purchase #7 $128.33   4.403%   $133.9804   $133.98   $134.00   $134.00  
  7 purchase totals = $929.17       $1,002.7157   $1,002.71   $1,002.75   $1,002.80