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 $85.28   12.796%   $96.1924   $96.19   $96.20   $96.20  
  Purchase #2 $116.30   3.661%   $120.5577   $120.56   $120.55   $120.60  
  Purchase #3 $60.46   6.109%   $64.1535   $64.15   $64.15   $64.20  
  Purchase #4 $231.42   10.755%   $256.3092   $256.31   $256.30   $256.30  
  Purchase #5 $195.39   5.543%   $206.2205   $206.22   $206.20   $206.20  
  Purchase #6 $130.85   8.508%   $141.9827   $141.98   $142.00   $142.00  
  Purchase #7 $241.47   4.595%   $252.5655   $252.57   $252.55   $252.60  
  7 purchase totals = $1,061.17       $1,137.9815   $1,137.98   $1,137.95   $1,138.10