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 $232.42   8.212%   $251.5063   $251.51   $251.50   $251.50  
  Purchase #2 $177.45   11.802%   $198.3926   $198.39   $198.40   $198.40  
  Purchase #3 $230.70   3.633%   $239.0813   $239.08   $239.10   $239.10  
  Purchase #4 $23.73   10.118%   $26.131   $26.13   $26.15   $26.10  
  Purchase #5 $209.26   4.287%   $218.231   $218.23   $218.25   $218.20  
  Purchase #6 $204.67   10.595%   $226.3548   $226.35   $226.35   $226.40  
  Purchase #7 $237.82   10.861%   $263.6496   $263.65   $263.65   $263.60  
  7 purchase totals = $1,316.05       $1,423.3466   $1,423.34   $1,423.40   $1,423.30