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 $131.58   6.160%   $139.6853   $139.69   $139.70   $139.70  
  Purchase #2 $48.85   7.797%   $52.6588   $52.66   $52.65   $52.70  
  Purchase #3 $235.93   4.547%   $246.6577   $246.66   $246.65   $246.70  
  Purchase #4 $199.58   11.164%   $221.8611   $221.86   $221.85   $221.90  
  Purchase #5 $224.96   5.581%   $237.515   $237.52   $237.50   $237.50  
  Purchase #6 $85.50   8.476%   $92.747   $92.75   $92.75   $92.70  
  Purchase #7 $67.69   13.162%   $76.5994   $76.60   $76.60   $76.60  
  7 purchase totals = $994.09       $1,067.7243   $1,067.74   $1,067.70   $1,067.80