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 $91.93   4.478%   $96.0466   $96.05   $96.05   $96.00  
  Purchase #2 $148.50   3.333%   $153.4495   $153.45   $153.45   $153.40  
  Purchase #3 $14.70   3.696%   $15.2433   $15.24   $15.25   $15.20  
  Purchase #4 $209.83   8.772%   $228.2363   $228.24   $228.25   $228.20  
  Purchase #5 $172.63   10.861%   $191.3793   $191.38   $191.40   $191.40  
  Purchase #6 $39.57   4.118%   $41.1995   $41.20   $41.20   $41.20  
  Purchase #7 $31.55   8.665%   $34.2838   $34.28   $34.30   $34.30  
  7 purchase totals = $708.71       $759.8383   $759.84   $759.90   $759.70