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 $62.39   11.281%   $69.4282   $69.43   $69.45   $69.40  
  Purchase #2 $249.81   9.461%   $273.4445   $273.44   $273.45   $273.40  
  Purchase #3 $233.46   9.395%   $255.3936   $255.39   $255.40   $255.40  
  Purchase #4 $96.64   4.127%   $100.6283   $100.63   $100.65   $100.60  
  Purchase #5 $46.39   11.748%   $51.8399   $51.84   $51.85   $51.80  
  Purchase #6 $129.44   13.320%   $146.6814   $146.68   $146.70   $146.70  
  Purchase #7 $160.92   5.457%   $169.7014   $169.70   $169.70   $169.70  
  7 purchase totals = $979.05       $1,067.1173   $1,067.11   $1,067.20   $1,067.00