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 $113.83   3.633%   $117.9654   $117.97   $117.95   $118.00  
  Purchase #2 $228.47   8.424%   $247.7163   $247.72   $247.70   $247.70  
  Purchase #3 $242.44   9.595%   $265.7021   $265.70   $265.70   $265.70  
  Purchase #4 $170.62   8.309%   $184.7968   $184.80   $184.80   $184.80  
  Purchase #5 $162.69   6.176%   $172.7377   $172.74   $172.75   $172.70  
  Purchase #6 $76.81   11.628%   $85.7415   $85.74   $85.75   $85.70  
  Purchase #7 $177.28   8.572%   $192.4764   $192.48   $192.50   $192.50  
  7 purchase totals = $1,172.14       $1,267.1362   $1,267.15   $1,267.15   $1,267.10