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 $62.54   6.172%   $66.4   $66.40   $66.40   $66.40  
  Purchase #2 $172.26   13.538%   $195.5806   $195.58   $195.60   $195.60  
  Purchase #3 $34.49   7.787%   $37.1757   $37.18   $37.20   $37.20  
  Purchase #4 $226.88   4.691%   $237.5229   $237.52   $237.50   $237.50  
  Purchase #5 $101.51   12.314%   $114.0099   $114.01   $114.00   $114.00  
  Purchase #6 $210.79   9.656%   $231.1439   $231.14   $231.15   $231.10  
  Purchase #7 $60.66   9.116%   $66.1898   $66.19   $66.20   $66.20  
  7 purchase totals = $869.13       $948.0228   $948.02   $948.05   $948.00