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 $160.98   10.163%   $177.3404   $177.34   $177.35   $177.30  
  Purchase #2 $71.34   6.525%   $75.9949   $75.99   $76.00   $76.00  
  Purchase #3 $53.98   6.575%   $57.5292   $57.53   $57.55   $57.50  
  Purchase #4 $55.68   12.823%   $62.8198   $62.82   $62.80   $62.80  
  Purchase #5 $115.31   3.592%   $119.4519   $119.45   $119.45   $119.50  
  Purchase #6 $196.85   4.677%   $206.0567   $206.06   $206.05   $206.10  
  Purchase #7 $205.96   7.543%   $221.4956   $221.50   $221.50   $221.50  
  7 purchase totals = $860.10       $920.6885   $920.69   $920.70   $920.70