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 $184.59   11.794%   $206.3605   $206.36   $206.35   $206.40  
  Purchase #2 $41.69   3.514%   $43.155   $43.16   $43.15   $43.20  
  Purchase #3 $200.30   8.183%   $216.6905   $216.69   $216.70   $216.70  
  Purchase #4 $189.48   11.483%   $211.238   $211.24   $211.25   $211.20  
  Purchase #5 $224.25   13.299%   $254.073   $254.07   $254.05   $254.10  
  Purchase #6 $139.42   12.129%   $156.3303   $156.33   $156.35   $156.30  
  Purchase #7 $5.32   7.249%   $5.7056   $5.71   $5.70   $5.70  
  7 purchase totals = $985.05       $1,093.5529   $1,093.56   $1,093.55   $1,093.60