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 $106.87   9.274%   $116.7811   $116.78   $116.80   $116.80  
  Purchase #2 $239.83   12.299%   $269.3267   $269.33   $269.35   $269.30  
  Purchase #3 $161.52   7.494%   $173.6243   $173.62   $173.60   $173.60  
  Purchase #4 $82.32   4.691%   $86.1816   $86.18   $86.20   $86.20  
  Purchase #5 $63.38   10.610%   $70.1046   $70.10   $70.10   $70.10  
  Purchase #6 $120.46   7.257%   $129.2018   $129.20   $129.20   $129.20  
  Purchase #7 $7.84   8.712%   $8.523   $8.52   $8.50   $8.50  
  7 purchase totals = $782.22       $853.7431   $853.73   $853.75   $853.70