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 $208.34   11.803%   $232.9304   $232.93   $232.95   $232.90  
  Purchase #2 $196.46   5.671%   $207.6012   $207.60   $207.60   $207.60  
  Purchase #3 $189.39   5.487%   $199.7818   $199.78   $199.80   $199.80  
  Purchase #4 $71.25   6.578%   $75.9368   $75.94   $75.95   $75.90  
  Purchase #5 $176.64   5.578%   $186.493   $186.49   $186.50   $186.50  
  Purchase #6 $130.25   12.838%   $146.9715   $146.97   $146.95   $147.00  
  Purchase #7 $207.58   9.254%   $226.7895   $226.79   $226.80   $226.80  
  7 purchase totals = $1,179.91       $1,276.5042   $1,276.50   $1,276.55   $1,276.50