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 $151.53   7.433%   $162.7932   $162.79   $162.80   $162.80  
  Purchase #2 $177.36   11.456%   $197.6784   $197.68   $197.70   $197.70  
  Purchase #3 $181.38   8.407%   $196.6286   $196.63   $196.65   $196.60  
  Purchase #4 $114.84   5.575%   $121.2423   $121.24   $121.25   $121.20  
  Purchase #5 $56.56   5.861%   $59.875   $59.88   $59.90   $59.90  
  Purchase #6 $192.25   9.200%   $209.937   $209.94   $209.95   $209.90  
  Purchase #7 $168.27   13.413%   $190.8401   $190.84   $190.85   $190.80  
  7 purchase totals = $1,042.19       $1,138.9946   $1,139.00   $1,139.10   $1,138.90