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 $92.38   6.793%   $98.6554   $98.66   $98.65   $98.70  
  Purchase #2 $184.35   5.790%   $195.0239   $195.02   $195.00   $195.00  
  Purchase #3 $246.43   9.756%   $270.4717   $270.47   $270.45   $270.50  
  Purchase #4 $149.59   9.557%   $163.8863   $163.89   $163.90   $163.90  
  Purchase #5 $175.46   4.798%   $183.8786   $183.88   $183.90   $183.90  
  Purchase #6 $85.60   11.864%   $95.7556   $95.76   $95.75   $95.80  
  Purchase #7 $172.37   7.825%   $185.858   $185.86   $185.85   $185.90  
  7 purchase totals = $1,106.18       $1,193.5295   $1,193.54   $1,193.50   $1,193.70