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 $191.28   13.865%   $217.801   $217.80   $217.80   $217.80  
  Purchase #2 $165.31   6.539%   $176.1196   $176.12   $176.10   $176.10  
  Purchase #3 $214.79   12.405%   $241.4347   $241.43   $241.45   $241.40  
  Purchase #4 $96.63   10.260%   $106.5442   $106.54   $106.55   $106.50  
  Purchase #5 $190.92   6.546%   $203.4176   $203.42   $203.40   $203.40  
  Purchase #6 $50.86   3.262%   $52.5191   $52.52   $52.50   $52.50  
  Purchase #7 $66.40   4.312%   $69.2632   $69.26   $69.25   $69.30  
  7 purchase totals = $976.19       $1,067.0994   $1,067.09   $1,067.05   $1,067.00