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 $15.52   4.719%   $16.2524   $16.25   $16.25   $16.30  
  Purchase #2 $134.98   6.647%   $143.9521   $143.95   $143.95   $144.00  
  Purchase #3 $206.68   8.435%   $224.1135   $224.11   $224.10   $224.10  
  Purchase #4 $248.84   8.112%   $269.0259   $269.03   $269.05   $269.00  
  Purchase #5 $241.29   7.209%   $258.6846   $258.68   $258.70   $258.70  
  Purchase #6 $114.46   11.834%   $128.0052   $128.01   $128.00   $128.00  
  Purchase #7 $47.53   12.146%   $53.303   $53.30   $53.30   $53.30  
  7 purchase totals = $1,009.30       $1,093.3367   $1,093.33   $1,093.35   $1,093.40