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 $70.52   8.511%   $76.522   $76.52   $76.50   $76.50  
  Purchase #2 $56.38   4.532%   $58.9351   $58.94   $58.95   $58.90  
  Purchase #3 $5.64   10.405%   $6.2268   $6.23   $6.25   $6.20  
  Purchase #4 $70.69   8.362%   $76.6011   $76.60   $76.60   $76.60  
  Purchase #5 $153.56   7.639%   $165.2904   $165.29   $165.30   $165.30  
  Purchase #6 $211.91   13.773%   $241.0964   $241.10   $241.10   $241.10  
  Purchase #7 $172.83   5.829%   $182.9043   $182.90   $182.90   $182.90  
  7 purchase totals = $741.53       $807.5761   $807.58   $807.60   $807.50