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 $120.58   11.194%   $134.0777   $134.08   $134.10   $134.10  
  Purchase #2 $160.59   13.240%   $181.8521   $181.85   $181.85   $181.90  
  Purchase #3 $136.93   13.600%   $155.5525   $155.55   $155.55   $155.60  
  Purchase #4 $174.63   7.341%   $187.4496   $187.45   $187.45   $187.40  
  Purchase #5 $68.31   3.468%   $70.679   $70.68   $70.70   $70.70  
  Purchase #6 $119.45   13.783%   $135.9138   $135.91   $135.90   $135.90  
  Purchase #7 $49.69   7.608%   $53.4704   $53.47   $53.45   $53.50  
  7 purchase totals = $830.18       $918.9951   $918.99   $919.00   $919.10