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 $175.88   12.733%   $198.2748   $198.27   $198.25   $198.30  
  Purchase #2 $58.92   4.333%   $61.473   $61.47   $61.45   $61.50  
  Purchase #3 $89.27   7.452%   $95.9224   $95.92   $95.90   $95.90  
  Purchase #4 $208.74   11.607%   $232.9685   $232.97   $232.95   $233.00  
  Purchase #5 $211.65   6.263%   $224.9056   $224.91   $224.90   $224.90  
  Purchase #6 $24.32   8.382%   $26.3585   $26.36   $26.35   $26.40  
  Purchase #7 $180.43   11.341%   $200.8926   $200.89   $200.90   $200.90  
  7 purchase totals = $949.21       $1,040.7954   $1,040.79   $1,040.70   $1,040.90