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 $61.89   12.720%   $69.7624   $69.76   $69.75   $69.80  
  Purchase #2 $176.42   13.227%   $199.7551   $199.76   $199.75   $199.80  
  Purchase #3 $98.48   4.493%   $102.9047   $102.90   $102.90   $102.90  
  Purchase #4 $8.37   6.179%   $8.8872   $8.89   $8.90   $8.90  
  Purchase #5 $150.39   10.288%   $165.8621   $165.86   $165.85   $165.90  
  Purchase #6 $233.60   8.716%   $253.9606   $253.96   $253.95   $254.00  
  Purchase #7 $239.73   3.108%   $247.1808   $247.18   $247.20   $247.20  
  7 purchase totals = $968.88       $1,048.3129   $1,048.31   $1,048.30   $1,048.50