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 $65.32   6.428%   $69.5188   $69.52   $69.50   $69.50  
  Purchase #2 $181.59   10.824%   $201.2453   $201.25   $201.25   $201.20  
  Purchase #3 $122.92   13.405%   $139.3974   $139.40   $139.40   $139.40  
  Purchase #4 $177.47   8.525%   $192.5993   $192.60   $192.60   $192.60  
  Purchase #5 $45.46   7.283%   $48.7709   $48.77   $48.75   $48.80  
  Purchase #6 $84.54   5.397%   $89.1026   $89.10   $89.10   $89.10  
  Purchase #7 $23.61   8.532%   $25.6244   $25.62   $25.60   $25.60  
  7 purchase totals = $700.91       $766.2587   $766.26   $766.20   $766.20