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 $236.53   7.706%   $254.757   $254.76   $254.75   $254.80  
  Purchase #2 $198.52   5.431%   $209.3016   $209.30   $209.30   $209.30  
  Purchase #3 $41.45   12.563%   $46.6574   $46.66   $46.65   $46.70  
  Purchase #4 $70.82   10.146%   $78.0054   $78.01   $78.00   $78.00  
  Purchase #5 $177.47   9.477%   $194.2888   $194.29   $194.30   $194.30  
  Purchase #6 $194.76   10.349%   $214.9157   $214.92   $214.90   $214.90  
  Purchase #7 $221.99   7.493%   $238.6237   $238.62   $238.60   $238.60  
  7 purchase totals = $1,141.54       $1,236.5496   $1,236.56   $1,236.50   $1,236.60