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 $91.70   5.163%   $96.4345   $96.43   $96.45   $96.40  
  Purchase #2 $11.33   8.755%   $12.3219   $12.32   $12.30   $12.30  
  Purchase #3 $109.99   5.539%   $116.0823   $116.08   $116.10   $116.10  
  Purchase #4 $187.59   7.854%   $202.3233   $202.32   $202.30   $202.30  
  Purchase #5 $212.82   13.305%   $241.1357   $241.14   $241.15   $241.10  
  Purchase #6 $218.61   13.619%   $248.3825   $248.38   $248.40   $248.40  
  Purchase #7 $102.57   9.839%   $112.6619   $112.66   $112.65   $112.70  
  7 purchase totals = $934.61       $1,029.3421   $1,029.33   $1,029.35   $1,029.30