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 $195.57   4.773%   $204.9046   $204.90   $204.90   $204.90  
  Purchase #2 $147.49   9.634%   $161.6992   $161.70   $161.70   $161.70  
  Purchase #3 $51.61   9.709%   $56.6208   $56.62   $56.60   $56.60  
  Purchase #4 $142.56   3.262%   $147.2103   $147.21   $147.20   $147.20  
  Purchase #5 $226.89   3.588%   $235.0308   $235.03   $235.05   $235.00  
  Purchase #6 $247.81   11.691%   $276.7815   $276.78   $276.80   $276.80  
  Purchase #7 $63.70   3.826%   $66.1372   $66.14   $66.15   $66.10  
  7 purchase totals = $1,075.63       $1,148.3844   $1,148.38   $1,148.40   $1,148.30