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 $201.27   5.296%   $211.9293   $211.93   $211.95   $211.90  
  Purchase #2 $141.31   9.225%   $154.3458   $154.35   $154.35   $154.30  
  Purchase #3 $146.48   10.184%   $161.3975   $161.40   $161.40   $161.40  
  Purchase #4 $89.80   3.459%   $92.9062   $92.91   $92.90   $92.90  
  Purchase #5 $115.60   8.580%   $125.5185   $125.52   $125.50   $125.50  
  Purchase #6 $241.54   11.256%   $268.7277   $268.73   $268.75   $268.70  
  Purchase #7 $118.32   4.386%   $123.5095   $123.51   $123.50   $123.50  
  7 purchase totals = $1,054.32       $1,138.3345   $1,138.35   $1,138.35   $1,138.20