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 $212.52   6.790%   $226.9501   $226.95   $226.95   $227.00  
  Purchase #2 $64.40   12.336%   $72.3444   $72.34   $72.35   $72.30  
  Purchase #3 $160.32   5.777%   $169.5817   $169.58   $169.60   $169.60  
  Purchase #4 $113.77   13.574%   $129.2131   $129.21   $129.20   $129.20  
  Purchase #5 $250.71   3.600%   $259.7356   $259.74   $259.75   $259.70  
  Purchase #6 $91.33   3.606%   $94.6234   $94.62   $94.60   $94.60  
  Purchase #7 $66.38   3.644%   $68.7989   $68.80   $68.80   $68.80  
  7 purchase totals = $959.43       $1,021.2472   $1,021.24   $1,021.25   $1,021.20