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 $62.74   4.708%   $65.6938   $65.69   $65.70   $65.70  
  Purchase #2 $6.30   3.304%   $6.5082   $6.51   $6.50   $6.50  
  Purchase #3 $208.65   12.560%   $234.8564   $234.86   $234.85   $234.90  
  Purchase #4 $67.55   4.407%   $70.5269   $70.53   $70.55   $70.50  
  Purchase #5 $110.86   3.416%   $114.647   $114.65   $114.65   $114.60  
  Purchase #6 $104.73   8.171%   $113.2875   $113.29   $113.30   $113.30  
  Purchase #7 $46.61   10.580%   $51.5413   $51.54   $51.55   $51.50  
  7 purchase totals = $607.44       $657.0611   $657.07   $657.10   $657.00