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 $209.91   7.671%   $226.0122   $226.01   $226.00   $226.00  
  Purchase #2 $177.63   13.503%   $201.6154   $201.62   $201.60   $201.60  
  Purchase #3 $6.76   4.438%   $7.06   $7.06   $7.05   $7.10  
  Purchase #4 $38.49   5.502%   $40.6077   $40.61   $40.60   $40.60  
  Purchase #5 $97.49   3.113%   $100.5249   $100.52   $100.50   $100.50  
  Purchase #6 $132.87   6.205%   $141.1146   $141.11   $141.10   $141.10  
  Purchase #7 $136.50   9.378%   $149.301   $149.30   $149.30   $149.30  
  7 purchase totals = $799.65       $866.2358   $866.23   $866.15   $866.20