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 $14.41   11.719%   $16.0987   $16.10   $16.10   $16.10  
  Purchase #2 $193.35   7.569%   $207.9847   $207.98   $208.00   $208.00  
  Purchase #3 $165.48   4.385%   $172.7363   $172.74   $172.75   $172.70  
  Purchase #4 $219.77   9.310%   $240.2306   $240.23   $240.25   $240.20  
  Purchase #5 $55.99   3.427%   $57.9088   $57.91   $57.90   $57.90  
  Purchase #6 $104.92   6.330%   $111.5614   $111.56   $111.55   $111.60  
  Purchase #7 $188.33   10.678%   $208.4399   $208.44   $208.45   $208.40  
  7 purchase totals = $942.25       $1,014.9604   $1,014.96   $1,015.00   $1,014.90