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 $51.73   9.458%   $56.6226   $56.62   $56.60   $56.60  
  Purchase #2 $153.93   12.831%   $173.6808   $173.68   $173.70   $173.70  
  Purchase #3 $234.86   3.228%   $242.4413   $242.44   $242.45   $242.40  
  Purchase #4 $212.92   7.342%   $228.5526   $228.55   $228.55   $228.60  
  Purchase #5 $40.90   6.769%   $43.6685   $43.67   $43.65   $43.70  
  Purchase #6 $248.30   10.327%   $273.9419   $273.94   $273.95   $273.90  
  Purchase #7 $192.95   8.829%   $209.9856   $209.99   $210.00   $210.00  
  7 purchase totals = $1,135.59       $1,228.8933   $1,228.89   $1,228.90   $1,228.90