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 $244.40   11.172%   $271.7044   $271.70   $271.70   $271.70  
  Purchase #2 $208.50   11.391%   $232.2502   $232.25   $232.25   $232.30  
  Purchase #3 $35.32   4.241%   $36.8179   $36.82   $36.80   $36.80  
  Purchase #4 $192.28   12.606%   $216.5188   $216.52   $216.50   $216.50  
  Purchase #5 $191.88   10.468%   $211.966   $211.97   $211.95   $212.00  
  Purchase #6 $78.84   12.863%   $88.9812   $88.98   $89.00   $89.00  
  Purchase #7 $163.70   8.526%   $177.6571   $177.66   $177.65   $177.70  
  7 purchase totals = $1,114.92       $1,235.8956   $1,235.90   $1,235.85   $1,236.00