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 $178.45   4.220%   $185.9806   $185.98   $186.00   $186.00  
  Purchase #2 $118.49   4.487%   $123.8066   $123.81   $123.80   $123.80  
  Purchase #3 $11.44   10.651%   $12.6585   $12.66   $12.65   $12.70  
  Purchase #4 $109.56   8.595%   $118.9767   $118.98   $119.00   $119.00  
  Purchase #5 $198.78   4.307%   $207.3415   $207.34   $207.35   $207.30  
  Purchase #6 $185.88   12.373%   $208.8789   $208.88   $208.90   $208.90  
  Purchase #7 $181.38   6.186%   $192.6002   $192.60   $192.60   $192.60  
  7 purchase totals = $983.98       $1,050.2430   $1,050.25   $1,050.30   $1,050.30