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 $181.48   6.716%   $193.6682   $193.67   $193.65   $193.70  
  Purchase #2 $126.88   4.182%   $132.1861   $132.19   $132.20   $132.20  
  Purchase #3 $85.59   9.419%   $93.6517   $93.65   $93.65   $93.70  
  Purchase #4 $246.33   4.159%   $256.5749   $256.57   $256.55   $256.60  
  Purchase #5 $125.86   3.775%   $130.6112   $130.61   $130.60   $130.60  
  Purchase #6 $248.31   8.528%   $269.4859   $269.49   $269.50   $269.50  
  Purchase #7 $86.93   4.309%   $90.6758   $90.68   $90.70   $90.70  
  7 purchase totals = $1,101.38       $1,166.8538   $1,166.86   $1,166.85   $1,167.00