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 $174.70   13.828%   $198.8575   $198.86   $198.85   $198.90  
  Purchase #2 $136.61   5.191%   $143.7014   $143.70   $143.70   $143.70  
  Purchase #3 $116.25   4.713%   $121.7289   $121.73   $121.75   $121.70  
  Purchase #4 $87.31   12.169%   $97.9348   $97.93   $97.95   $97.90  
  Purchase #5 $216.93   5.834%   $229.5857   $229.59   $229.60   $229.60  
  Purchase #6 $167.88   9.215%   $183.3501   $183.35   $183.35   $183.40  
  Purchase #7 $24.50   7.542%   $26.3478   $26.35   $26.35   $26.30  
  7 purchase totals = $924.18       $1,001.5062   $1,001.51   $1,001.55   $1,001.50