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 $88.82   8.725%   $96.5695   $96.57   $96.55   $96.60  
  Purchase #2 $190.72   6.638%   $203.38   $203.38   $203.40   $203.40  
  Purchase #3 $88.59   6.378%   $94.2403   $94.24   $94.25   $94.20  
  Purchase #4 $14.69   11.585%   $16.3918   $16.39   $16.40   $16.40  
  Purchase #5 $201.54   7.396%   $216.4459   $216.45   $216.45   $216.40  
  Purchase #6 $9.71   10.542%   $10.7336   $10.73   $10.75   $10.70  
  Purchase #7 $145.57   11.166%   $161.8243   $161.82   $161.80   $161.80  
  7 purchase totals = $739.64       $799.5854   $799.58   $799.60   $799.50