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 $61.40   8.682%   $66.7307   $66.73   $66.75   $66.70  
  Purchase #2 $229.58   4.229%   $239.2889   $239.29   $239.30   $239.30  
  Purchase #3 $97.32   4.103%   $101.313   $101.31   $101.30   $101.30  
  Purchase #4 $126.88   12.396%   $142.608   $142.61   $142.60   $142.60  
  Purchase #5 $160.46   4.595%   $167.8331   $167.83   $167.85   $167.80  
  Purchase #6 $65.30   5.717%   $69.0332   $69.03   $69.05   $69.00  
  Purchase #7 $239.79   3.709%   $248.6838   $248.68   $248.70   $248.70  
  7 purchase totals = $980.73       $1,035.4907   $1,035.48   $1,035.55   $1,035.40