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 $156.52   11.469%   $174.4713   $174.47   $174.45   $174.50  
  Purchase #2 $32.65   10.854%   $36.1938   $36.19   $36.20   $36.20  
  Purchase #3 $244.51   9.225%   $267.066   $267.07   $267.05   $267.10  
  Purchase #4 $143.29   7.183%   $153.5825   $153.58   $153.60   $153.60  
  Purchase #5 $44.80   3.844%   $46.5221   $46.52   $46.50   $46.50  
  Purchase #6 $78.50   9.554%   $85.9999   $86.00   $86.00   $86.00  
  Purchase #7 $151.60   8.688%   $164.771   $164.77   $164.75   $164.80  
  7 purchase totals = $851.87       $928.6066   $928.60   $928.55   $928.70