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 $219.99   6.664%   $234.6501   $234.65   $234.65   $234.70  
  Purchase #2 $56.84   6.790%   $60.6994   $60.70   $60.70   $60.70  
  Purchase #3 $68.37   9.434%   $74.82   $74.82   $74.80   $74.80  
  Purchase #4 $203.44   6.682%   $217.0339   $217.03   $217.05   $217.00  
  Purchase #5 $99.42   9.689%   $109.0528   $109.05   $109.05   $109.10  
  Purchase #6 $76.40   12.476%   $85.9317   $85.93   $85.95   $85.90  
  Purchase #7 $237.61   10.670%   $262.963   $262.96   $262.95   $263.00  
  7 purchase totals = $962.07       $1,045.1509   $1,045.14   $1,045.15   $1,045.20