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 $189.44   6.711%   $202.1533   $202.15   $202.15   $202.20  
  Purchase #2 $72.49   8.359%   $78.5494   $78.55   $78.55   $78.50  
  Purchase #3 $122.56   3.280%   $126.58   $126.58   $126.60   $126.60  
  Purchase #4 $154.43   5.691%   $163.2186   $163.22   $163.20   $163.20  
  Purchase #5 $179.57   11.566%   $200.3391   $200.34   $200.35   $200.30  
  Purchase #6 $32.72   11.568%   $36.505   $36.51   $36.50   $36.50  
  Purchase #7 $45.70   5.488%   $48.208   $48.21   $48.20   $48.20  
  7 purchase totals = $796.91       $855.5534   $855.56   $855.55   $855.50