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 $163.91   8.390%   $177.662   $177.66   $177.65   $177.70  
  Purchase #2 $77.33   9.494%   $84.6717   $84.67   $84.65   $84.70  
  Purchase #3 $36.57   11.472%   $40.7653   $40.77   $40.75   $40.80  
  Purchase #4 $41.66   13.872%   $47.4391   $47.44   $47.45   $47.40  
  Purchase #5 $250.31   9.329%   $273.6614   $273.66   $273.65   $273.70  
  Purchase #6 $196.99   3.647%   $204.1742   $204.17   $204.15   $204.20  
  Purchase #7 $196.76   4.304%   $205.2286   $205.23   $205.25   $205.20  
  7 purchase totals = $963.53       $1,033.6023   $1,033.60   $1,033.55   $1,033.70