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 $13.76   8.273%   $14.8984   $14.90   $14.90   $14.90  
  Purchase #2 $43.62   10.617%   $48.2511   $48.25   $48.25   $48.30  
  Purchase #3 $118.42   7.507%   $127.3098   $127.31   $127.30   $127.30  
  Purchase #4 $88.73   8.181%   $95.989   $95.99   $96.00   $96.00  
  Purchase #5 $247.52   9.735%   $271.6161   $271.62   $271.60   $271.60  
  Purchase #6 $121.50   9.770%   $133.3706   $133.37   $133.35   $133.40  
  Purchase #7 $115.59   9.627%   $126.7178   $126.72   $126.70   $126.70  
  7 purchase totals = $749.14       $818.1528   $818.16   $818.10   $818.20