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 $190.46   12.494%   $214.2561   $214.26   $214.25   $214.30  
  Purchase #2 $112.95   10.149%   $124.4133   $124.41   $124.40   $124.40  
  Purchase #3 $115.62   13.639%   $131.3894   $131.39   $131.40   $131.40  
  Purchase #4 $192.94   5.485%   $203.5228   $203.52   $203.50   $203.50  
  Purchase #5 $62.31   4.336%   $65.0118   $65.01   $65.00   $65.00  
  Purchase #6 $117.61   11.569%   $131.2163   $131.22   $131.20   $131.20  
  Purchase #7 $177.65   5.466%   $187.3603   $187.36   $187.35   $187.40  
  7 purchase totals = $969.54       $1,057.1700   $1,057.17   $1,057.10   $1,057.20