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 $84.62   10.234%   $93.28   $93.28   $93.30   $93.30  
  Purchase #2 $93.89   9.862%   $103.1494   $103.15   $103.15   $103.10  
  Purchase #3 $228.58   8.395%   $247.7693   $247.77   $247.75   $247.80  
  Purchase #4 $173.83   11.582%   $193.963   $193.96   $193.95   $194.00  
  Purchase #5 $170.85   7.873%   $184.301   $184.30   $184.30   $184.30  
  Purchase #6 $107.38   9.608%   $117.6971   $117.70   $117.70   $117.70  
  Purchase #7 $85.77   11.324%   $95.4826   $95.48   $95.50   $95.50  
  7 purchase totals = $944.92       $1,035.6424   $1,035.64   $1,035.65   $1,035.70