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 $212.58   7.396%   $228.3024   $228.30   $228.30   $228.30  
  Purchase #2 $233.87   3.626%   $242.3501   $242.35   $242.35   $242.40  
  Purchase #3 $161.99   4.102%   $168.6348   $168.63   $168.65   $168.60  
  Purchase #4 $150.98   12.429%   $169.7453   $169.75   $169.75   $169.70  
  Purchase #5 $246.99   6.363%   $262.706   $262.71   $262.70   $262.70  
  Purchase #6 $158.80   6.617%   $169.3078   $169.31   $169.30   $169.30  
  Purchase #7 $88.78   11.813%   $99.2676   $99.27   $99.25   $99.30  
  7 purchase totals = $1,253.99       $1,340.3140   $1,340.32   $1,340.30   $1,340.30