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 $151.97   10.204%   $167.477   $167.48   $167.50   $167.50  
  Purchase #2 $225.54   7.269%   $241.9345   $241.93   $241.95   $241.90  
  Purchase #3 $74.34   5.580%   $78.4882   $78.49   $78.50   $78.50  
  Purchase #4 $33.58   7.396%   $36.0636   $36.06   $36.05   $36.10  
  Purchase #5 $133.74   3.770%   $138.782   $138.78   $138.80   $138.80  
  Purchase #6 $162.59   7.622%   $174.9826   $174.98   $175.00   $175.00  
  Purchase #7 $65.83   11.254%   $73.2385   $73.24   $73.25   $73.20  
  7 purchase totals = $847.59       $910.9664   $910.96   $911.05   $911.00