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 $84.83   12.187%   $95.1682   $95.17   $95.15   $95.20  
  Purchase #2 $44.83   6.553%   $47.7677   $47.77   $47.75   $47.80  
  Purchase #3 $52.31   7.746%   $56.3619   $56.36   $56.35   $56.40  
  Purchase #4 $88.95   10.578%   $98.3591   $98.36   $98.35   $98.40  
  Purchase #5 $139.74   11.814%   $156.2489   $156.25   $156.25   $156.20  
  Purchase #6 $198.77   13.608%   $225.8186   $225.82   $225.80   $225.80  
  Purchase #7 $159.93   5.556%   $168.8157   $168.82   $168.80   $168.80  
  7 purchase totals = $769.36       $848.5401   $848.55   $848.45   $848.60