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 $171.58   13.610%   $194.932   $194.93   $194.95   $194.90  
  Purchase #2 $52.84   5.782%   $55.8952   $55.90   $55.90   $55.90  
  Purchase #3 $104.32   8.202%   $112.8763   $112.88   $112.90   $112.90  
  Purchase #4 $248.80   8.293%   $269.433   $269.43   $269.45   $269.40  
  Purchase #5 $35.79   7.292%   $38.3998   $38.40   $38.40   $38.40  
  Purchase #6 $229.66   6.537%   $244.6729   $244.67   $244.65   $244.70  
  Purchase #7 $205.73   8.160%   $222.5176   $222.52   $222.50   $222.50  
  7 purchase totals = $1,048.72       $1,138.7268   $1,138.73   $1,138.75   $1,138.70