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 $183.85   12.608%   $207.0298   $207.03   $207.05   $207.00  
  Purchase #2 $81.25   5.122%   $85.4116   $85.41   $85.40   $85.40  
  Purchase #3 $153.47   10.826%   $170.0847   $170.08   $170.10   $170.10  
  Purchase #4 $44.52   5.110%   $46.795   $46.80   $46.80   $46.80  
  Purchase #5 $127.69   5.541%   $134.7653   $134.77   $134.75   $134.80  
  Purchase #6 $243.31   4.320%   $253.821   $253.82   $253.80   $253.80  
  Purchase #7 $155.29   10.476%   $171.5582   $171.56   $171.55   $171.60  
  7 purchase totals = $989.38       $1,069.4656   $1,069.47   $1,069.45   $1,069.50