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 $182.39   10.543%   $201.6194   $201.62   $201.60   $201.60  
  Purchase #2 $55.52   4.181%   $57.8413   $57.84   $57.85   $57.80  
  Purchase #3 $53.27   8.522%   $57.8097   $57.81   $57.80   $57.80  
  Purchase #4 $202.39   11.340%   $225.341   $225.34   $225.35   $225.30  
  Purchase #5 $248.56   6.642%   $265.0694   $265.07   $265.05   $265.10  
  Purchase #6 $101.43   11.748%   $113.346   $113.35   $113.35   $113.30  
  Purchase #7 $240.46   12.120%   $269.6038   $269.60   $269.60   $269.60  
  7 purchase totals = $1,084.02       $1,190.6306   $1,190.63   $1,190.60   $1,190.50