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 $156.75   5.856%   $165.9293   $165.93   $165.95   $165.90  
  Purchase #2 $240.82   13.603%   $273.5787   $273.58   $273.60   $273.60  
  Purchase #3 $117.89   9.116%   $128.6369   $128.64   $128.65   $128.60  
  Purchase #4 $87.91   5.621%   $92.8514   $92.85   $92.85   $92.90  
  Purchase #5 $62.73   6.873%   $67.0414   $67.04   $67.05   $67.00  
  Purchase #6 $60.31   3.310%   $62.3063   $62.31   $62.30   $62.30  
  Purchase #7 $229.77   3.261%   $237.2628   $237.26   $237.25   $237.30  
  7 purchase totals = $956.18       $1,027.6068   $1,027.61   $1,027.65   $1,027.60