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 $60.49   10.102%   $66.6007   $66.60   $66.60   $66.60  
  Purchase #2 $238.64   13.784%   $271.5341   $271.53   $271.55   $271.50  
  Purchase #3 $104.29   10.773%   $115.5252   $115.53   $115.55   $115.50  
  Purchase #4 $198.99   3.416%   $205.7875   $205.79   $205.80   $205.80  
  Purchase #5 $206.31   9.678%   $226.2767   $226.28   $226.30   $226.30  
  Purchase #6 $159.71   13.847%   $181.825   $181.83   $181.85   $181.80  
  Purchase #7 $90.64   7.264%   $97.2241   $97.22   $97.20   $97.20  
  7 purchase totals = $1,059.07       $1,164.7733   $1,164.78   $1,164.85   $1,164.70