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 $94.47   8.314%   $102.3242   $102.32   $102.30   $102.30  
  Purchase #2 $174.47   9.814%   $191.5925   $191.59   $191.60   $191.60  
  Purchase #3 $157.86   11.794%   $176.478   $176.48   $176.50   $176.50  
  Purchase #4 $219.96   12.859%   $248.2447   $248.24   $248.25   $248.20  
  Purchase #5 $103.90   6.188%   $110.3293   $110.33   $110.35   $110.30  
  Purchase #6 $192.90   13.759%   $219.4411   $219.44   $219.45   $219.40  
  Purchase #7 $54.58   4.175%   $56.8587   $56.86   $56.85   $56.90  
  7 purchase totals = $998.14       $1,105.2685   $1,105.26   $1,105.30   $1,105.20