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 $205.75   10.462%   $227.2756   $227.28   $227.30   $227.30  
  Purchase #2 $67.78   13.246%   $76.7581   $76.76   $76.75   $76.80  
  Purchase #3 $106.89   9.827%   $117.3941   $117.39   $117.40   $117.40  
  Purchase #4 $149.85   13.384%   $169.9059   $169.91   $169.90   $169.90  
  Purchase #5 $127.37   13.102%   $144.058   $144.06   $144.05   $144.10  
  Purchase #6 $221.85   11.667%   $247.7332   $247.73   $247.75   $247.70  
  Purchase #7 $152.86   10.688%   $169.1977   $169.20   $169.20   $169.20  
  7 purchase totals = $1,032.35       $1,152.3226   $1,152.33   $1,152.35   $1,152.40