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 $119.46   13.459%   $135.5381   $135.54   $135.55   $135.50  
  Purchase #2 $26.50   11.167%   $29.4593   $29.46   $29.45   $29.50  
  Purchase #3 $130.29   3.153%   $134.398   $134.40   $134.40   $134.40  
  Purchase #4 $167.56   8.558%   $181.8998   $181.90   $181.90   $181.90  
  Purchase #5 $24.42   8.661%   $26.535   $26.54   $26.55   $26.50  
  Purchase #6 $163.78   9.751%   $179.7502   $179.75   $179.75   $179.80  
  Purchase #7 $150.58   11.410%   $167.7612   $167.76   $167.75   $167.80  
  7 purchase totals = $782.59       $855.3416   $855.35   $855.35   $855.40