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 $70.91   5.595%   $74.8774   $74.88   $74.90   $74.90  
  Purchase #2 $213.86   4.353%   $223.1693   $223.17   $223.15   $223.20  
  Purchase #3 $113.54   6.165%   $120.5397   $120.54   $120.55   $120.50  
  Purchase #4 $181.35   9.401%   $198.3987   $198.40   $198.40   $198.40  
  Purchase #5 $216.61   11.313%   $241.1151   $241.12   $241.10   $241.10  
  Purchase #6 $53.73   5.254%   $56.553   $56.55   $56.55   $56.60  
  Purchase #7 $61.26   13.746%   $69.6808   $69.68   $69.70   $69.70  
  7 purchase totals = $911.26       $984.3340   $984.34   $984.35   $984.40