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 $123.41   13.108%   $139.5866   $139.59   $139.60   $139.60  
  Purchase #2 $104.58   12.208%   $117.3471   $117.35   $117.35   $117.30  
  Purchase #3 $224.36   6.560%   $239.078   $239.08   $239.10   $239.10  
  Purchase #4 $204.53   9.847%   $224.6701   $224.67   $224.65   $224.70  
  Purchase #5 $167.37   8.382%   $181.399   $181.40   $181.40   $181.40  
  Purchase #6 $144.64   8.379%   $156.7594   $156.76   $156.75   $156.80  
  Purchase #7 $125.97   7.239%   $135.089   $135.09   $135.10   $135.10  
  7 purchase totals = $1,094.86       $1,193.9292   $1,193.94   $1,193.95   $1,194.00