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 $141.44   3.255%   $146.0439   $146.04   $146.05   $146.00  
  Purchase #2 $209.59   7.869%   $226.0826   $226.08   $226.10   $226.10  
  Purchase #3 $10.45   6.649%   $11.1448   $11.14   $11.15   $11.10  
  Purchase #4 $73.31   4.314%   $76.4726   $76.47   $76.45   $76.50  
  Purchase #5 $167.31   9.847%   $183.785   $183.79   $183.80   $183.80  
  Purchase #6 $114.59   10.542%   $126.6701   $126.67   $126.65   $126.70  
  Purchase #7 $211.27   6.208%   $224.3856   $224.39   $224.40   $224.40  
  7 purchase totals = $927.96       $994.5846   $994.58   $994.60   $994.60