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 $238.91   10.842%   $264.8126   $264.81   $264.80   $264.80  
  Purchase #2 $197.31   11.757%   $220.5077   $220.51   $220.50   $220.50  
  Purchase #3 $71.86   13.852%   $81.814   $81.81   $81.80   $81.80  
  Purchase #4 $143.66   13.310%   $162.7811   $162.78   $162.80   $162.80  
  Purchase #5 $167.34   5.288%   $176.1889   $176.19   $176.20   $176.20  
  Purchase #6 $136.88   13.355%   $155.1603   $155.16   $155.15   $155.20  
  Purchase #7 $116.55   12.605%   $131.2411   $131.24   $131.25   $131.20  
  7 purchase totals = $1,072.51       $1,192.5057   $1,192.50   $1,192.50   $1,192.50