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 $202.90   5.648%   $214.3598   $214.36   $214.35   $214.40  
  Purchase #2 $110.86   3.406%   $114.6359   $114.64   $114.65   $114.60  
  Purchase #3 $94.80   6.456%   $100.9203   $100.92   $100.90   $100.90  
  Purchase #4 $41.66   5.145%   $43.8034   $43.80   $43.80   $43.80  
  Purchase #5 $240.74   4.693%   $252.0379   $252.04   $252.05   $252.00  
  Purchase #6 $90.36   8.827%   $98.3361   $98.34   $98.35   $98.30  
  Purchase #7 $160.79   7.736%   $173.2287   $173.23   $173.25   $173.20  
  7 purchase totals = $942.11       $997.3221   $997.33   $997.35   $997.20