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 $60.87   9.577%   $66.6995   $66.70   $66.70   $66.70  
  Purchase #2 $8.62   11.557%   $9.6162   $9.62   $9.60   $9.60  
  Purchase #3 $177.69   9.357%   $194.3165   $194.32   $194.30   $194.30  
  Purchase #4 $51.84   4.415%   $54.1287   $54.13   $54.15   $54.10  
  Purchase #5 $218.30   9.631%   $239.3245   $239.32   $239.30   $239.30  
  Purchase #6 $13.33   8.641%   $14.4818   $14.48   $14.50   $14.50  
  Purchase #7 $191.64   11.153%   $213.0136   $213.01   $213.00   $213.00  
  7 purchase totals = $722.29       $791.5808   $791.58   $791.55   $791.50