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 $56.97   8.104%   $61.5868   $61.59   $61.60   $61.60  
  Purchase #2 $33.45   6.296%   $35.556   $35.56   $35.55   $35.60  
  Purchase #3 $176.25   8.355%   $190.9757   $190.98   $191.00   $191.00  
  Purchase #4 $167.83   8.342%   $181.8304   $181.83   $181.85   $181.80  
  Purchase #5 $203.66   3.210%   $210.1975   $210.20   $210.20   $210.20  
  Purchase #6 $38.48   8.461%   $41.7358   $41.74   $41.75   $41.70  
  Purchase #7 $12.67   12.479%   $14.2511   $14.25   $14.25   $14.30  
  7 purchase totals = $689.31       $736.1333   $736.15   $736.20   $736.20