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 $74.58   10.102%   $82.1141   $82.11   $82.10   $82.10  
  Purchase #2 $183.84   10.828%   $203.7462   $203.75   $203.75   $203.70  
  Purchase #3 $99.84   13.705%   $113.5231   $113.52   $113.50   $113.50  
  Purchase #4 $230.54   3.213%   $237.9473   $237.95   $237.95   $237.90  
  Purchase #5 $224.60   12.715%   $253.1579   $253.16   $253.15   $253.20  
  Purchase #6 $156.81   11.841%   $175.3779   $175.38   $175.40   $175.40  
  Purchase #7 $55.71   10.598%   $61.6141   $61.61   $61.60   $61.60  
  7 purchase totals = $1,025.92       $1,127.4806   $1,127.48   $1,127.45   $1,127.40