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 $104.58   10.422%   $115.4793   $115.48   $115.50   $115.50  
  Purchase #2 $225.84   12.314%   $253.6499   $253.65   $253.65   $253.60  
  Purchase #3 $169.46   6.527%   $180.5207   $180.52   $180.50   $180.50  
  Purchase #4 $70.62   4.675%   $73.9215   $73.92   $73.90   $73.90  
  Purchase #5 $159.51   11.701%   $178.1743   $178.17   $178.15   $178.20  
  Purchase #6 $221.26   9.688%   $242.6957   $242.70   $242.70   $242.70  
  Purchase #7 $117.50   3.116%   $121.1613   $121.16   $121.15   $121.20  
  7 purchase totals = $1,068.77       $1,165.6027   $1,165.60   $1,165.55   $1,165.60