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 $54.88   3.584%   $56.8469   $56.85   $56.85   $56.80  
  Purchase #2 $192.55   6.802%   $205.6473   $205.65   $205.65   $205.60  
  Purchase #3 $194.52   8.756%   $211.5522   $211.55   $211.55   $211.60  
  Purchase #4 $67.86   10.407%   $74.9222   $74.92   $74.90   $74.90  
  Purchase #5 $171.55   7.412%   $184.2653   $184.27   $184.25   $184.30  
  Purchase #6 $241.76   7.423%   $259.7058   $259.71   $259.70   $259.70  
  Purchase #7 $71.62   3.652%   $74.2356   $74.24   $74.25   $74.20  
  7 purchase totals = $994.74       $1,067.1753   $1,067.19   $1,067.15   $1,067.10