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 $64.46   8.509%   $69.9449   $69.94   $69.95   $69.90  
  Purchase #2 $193.51   5.581%   $204.3098   $204.31   $204.30   $204.30  
  Purchase #3 $115.67   5.212%   $121.6987   $121.70   $121.70   $121.70  
  Purchase #4 $155.81   4.507%   $162.8324   $162.83   $162.85   $162.80  
  Purchase #5 $65.79   4.526%   $68.7677   $68.77   $68.75   $68.80  
  Purchase #6 $48.65   11.869%   $54.4243   $54.42   $54.40   $54.40  
  Purchase #7 $131.58   12.133%   $147.5446   $147.54   $147.55   $147.50  
  7 purchase totals = $775.47       $829.5224   $829.51   $829.50   $829.40