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 $83.48   11.757%   $93.2947   $93.29   $93.30   $93.30  
  Purchase #2 $153.55   3.764%   $159.3296   $159.33   $159.35   $159.30  
  Purchase #3 $219.33   6.397%   $233.3605   $233.36   $233.35   $233.40  
  Purchase #4 $116.92   6.776%   $124.8425   $124.84   $124.85   $124.80  
  Purchase #5 $97.46   5.353%   $102.677   $102.68   $102.70   $102.70  
  Purchase #6 $156.85   11.318%   $174.6023   $174.60   $174.60   $174.60  
  Purchase #7 $96.83   3.858%   $100.5657   $100.57   $100.55   $100.60  
  7 purchase totals = $924.42       $988.6723   $988.67   $988.70   $988.70