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 $11.33   11.279%   $12.6079   $12.61   $12.60   $12.60  
  Purchase #2 $124.63   9.274%   $136.1882   $136.19   $136.20   $136.20  
  Purchase #3 $241.73   11.844%   $270.3605   $270.36   $270.35   $270.40  
  Purchase #4 $219.52   5.396%   $231.3653   $231.37   $231.35   $231.40  
  Purchase #5 $36.37   11.483%   $40.5464   $40.55   $40.55   $40.50  
  Purchase #6 $124.26   13.763%   $141.3619   $141.36   $141.35   $141.40  
  Purchase #7 $176.37   12.614%   $198.6173   $198.62   $198.60   $198.60  
  7 purchase totals = $934.21       $1,031.0475   $1,031.06   $1,031.00   $1,031.10