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 $29.34   13.739%   $33.371   $33.37   $33.35   $33.40  
  Purchase #2 $232.97   5.462%   $245.6948   $245.69   $245.70   $245.70  
  Purchase #3 $64.57   4.244%   $67.3104   $67.31   $67.30   $67.30  
  Purchase #4 $114.81   9.435%   $125.6423   $125.64   $125.65   $125.60  
  Purchase #5 $53.87   13.230%   $60.997   $61.00   $61.00   $61.00  
  Purchase #6 $153.37   12.585%   $172.6716   $172.67   $172.65   $172.70  
  Purchase #7 $198.32   11.252%   $220.635   $220.64   $220.65   $220.60  
  7 purchase totals = $847.25       $926.3221   $926.32   $926.30   $926.30