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 $136.98   4.397%   $143.003   $143.00   $143.00   $143.00  
  Purchase #2 $68.65   3.104%   $70.7809   $70.78   $70.80   $70.80  
  Purchase #3 $140.79   4.585%   $147.2452   $147.25   $147.25   $147.20  
  Purchase #4 $119.84   4.569%   $125.3155   $125.32   $125.30   $125.30  
  Purchase #5 $211.66   3.468%   $219.0004   $219.00   $219.00   $219.00  
  Purchase #6 $107.77   6.729%   $115.0218   $115.02   $115.00   $115.00  
  Purchase #7 $176.55   8.132%   $190.907   $190.91   $190.90   $190.90  
  7 purchase totals = $962.24       $1,011.2738   $1,011.28   $1,011.25   $1,011.20