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 $12.94   13.150%   $14.6416   $14.64   $14.65   $14.60  
  Purchase #2 $114.36   10.691%   $126.5862   $126.59   $126.60   $126.60  
  Purchase #3 $181.37   11.190%   $201.6653   $201.67   $201.65   $201.70  
  Purchase #4 $64.66   11.435%   $72.0539   $72.05   $72.05   $72.10  
  Purchase #5 $67.87   8.615%   $73.717   $73.72   $73.70   $73.70  
  Purchase #6 $85.70   11.564%   $95.6103   $95.61   $95.60   $95.60  
  Purchase #7 $207.65   12.193%   $232.9688   $232.97   $232.95   $233.00  
  7 purchase totals = $734.55       $817.2431   $817.25   $817.20   $817.30