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 $238.52   11.529%   $266.019   $266.02   $266.00   $266.00  
  Purchase #2 $131.86   12.448%   $148.2739   $148.27   $148.25   $148.30  
  Purchase #3 $156.91   4.493%   $163.96   $163.96   $163.95   $164.00  
  Purchase #4 $149.87   3.812%   $155.583   $155.58   $155.60   $155.60  
  Purchase #5 $136.58   3.428%   $141.262   $141.26   $141.25   $141.30  
  Purchase #6 $37.88   7.476%   $40.7119   $40.71   $40.70   $40.70  
  Purchase #7 $19.59   5.483%   $20.6641   $20.66   $20.65   $20.70  
  7 purchase totals = $871.21       $936.4739   $936.46   $936.40   $936.60