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 $65.61   6.336%   $69.767   $69.77   $69.75   $69.80  
  Purchase #2 $23.66   4.459%   $24.715   $24.72   $24.70   $24.70  
  Purchase #3 $243.56   3.566%   $252.2453   $252.25   $252.25   $252.20  
  Purchase #4 $233.74   4.267%   $243.7137   $243.71   $243.70   $243.70  
  Purchase #5 $70.32   11.702%   $78.5488   $78.55   $78.55   $78.50  
  Purchase #6 $113.79   12.405%   $127.9056   $127.91   $127.90   $127.90  
  Purchase #7 $238.44   3.792%   $247.4816   $247.48   $247.50   $247.50  
  7 purchase totals = $989.12       $1,044.3770   $1,044.39   $1,044.35   $1,044.30