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 $59.45   7.284%   $63.7803   $63.78   $63.80   $63.80  
  Purchase #2 $240.69   13.385%   $272.9064   $272.91   $272.90   $272.90  
  Purchase #3 $40.50   10.416%   $44.7185   $44.72   $44.70   $44.70  
  Purchase #4 $90.36   13.560%   $102.6128   $102.61   $102.60   $102.60  
  Purchase #5 $228.56   4.867%   $239.684   $239.68   $239.70   $239.70  
  Purchase #6 $130.25   4.138%   $135.6397   $135.64   $135.65   $135.60  
  Purchase #7 $165.36   3.388%   $170.9624   $170.96   $170.95   $171.00  
  7 purchase totals = $955.17       $1,030.3041   $1,030.30   $1,030.30   $1,030.30