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 $64.73   3.511%   $67.0027   $67.00   $67.00   $67.00  
  Purchase #2 $23.49   8.783%   $25.5531   $25.55   $25.55   $25.60  
  Purchase #3 $116.58   13.315%   $132.1026   $132.10   $132.10   $132.10  
  Purchase #4 $150.60   11.869%   $168.4747   $168.47   $168.45   $168.50  
  Purchase #5 $235.69   5.231%   $248.0189   $248.02   $248.00   $248.00  
  Purchase #6 $124.29   13.112%   $140.5869   $140.59   $140.60   $140.60  
  Purchase #7 $173.89   7.445%   $186.8361   $186.84   $186.85   $186.80  
  7 purchase totals = $889.27       $968.5750   $968.57   $968.55   $968.60