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 $72.67   11.816%   $81.2567   $81.26   $81.25   $81.30  
  Purchase #2 $158.79   9.629%   $174.0799   $174.08   $174.10   $174.10  
  Purchase #3 $113.36   5.191%   $119.2445   $119.24   $119.25   $119.20  
  Purchase #4 $170.75   11.674%   $190.6834   $190.68   $190.70   $190.70  
  Purchase #5 $204.75   12.483%   $230.3089   $230.31   $230.30   $230.30  
  Purchase #6 $157.44   8.242%   $170.4162   $170.42   $170.40   $170.40  
  Purchase #7 $189.33   8.430%   $205.2905   $205.29   $205.30   $205.30  
  7 purchase totals = $1,067.09       $1,171.2801   $1,171.28   $1,171.30   $1,171.30