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 $28.58   13.838%   $32.5349   $32.53   $32.55   $32.50  
  Purchase #2 $177.42   13.830%   $201.9572   $201.96   $201.95   $202.00  
  Purchase #3 $246.31   6.751%   $262.9384   $262.94   $262.95   $262.90  
  Purchase #4 $184.27   5.206%   $193.8631   $193.86   $193.85   $193.90  
  Purchase #5 $55.78   8.104%   $60.3004   $60.30   $60.30   $60.30  
  Purchase #6 $107.64   13.675%   $122.3598   $122.36   $122.35   $122.40  
  Purchase #7 $33.76   10.232%   $37.2143   $37.21   $37.20   $37.20  
  7 purchase totals = $833.76       $911.1681   $911.16   $911.15   $911.20